WIX 57055 filter vs. Subaru Oil Pump/Filter Compatibility Analysis: Please help me make this correct!

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A lot of folks have gone in circles with this very thing especially regarding the Subaru oil bypass and flow rates. Ultimately I think you’ll be fine with whatever you decide. For myself my preference is OEM. If that’s unavailable or I’m feeling like grabbing something else I like the O’Reily’s MicroGard Select. Often a good deal with their oil+filter specials. Another consideration I don’t see often here are FULL filters. NAPA sells this brand. I haven’t tried them yet, but many folks running asian vehicles seem to like them.

Cheers!
I understand that OP may find this topic confusing, and lots of strong words and private tears have been shed on this. However, if one looks at the OEM filter (either version) and then compares the construction, materials, & inlet hole sizes, one can conclude that literally any aftermarket filter will work fine.

As always, you can go upmarket and buy a wire-backed filter for strength, or you could even buy a $2 Prime Guard but just understand the media has a much lower loading capacity.

I’m not saying they don’t exist, but I don’t remember any Subaru failures that could be traced to the oil filter (@Trav…?). Subarus have had head gaskets, rod bearings on turbos, some issues with smaller gears in the oil pump that Trav shared, and some oil ring issues on FBs, but filters… nah.

Best of luck though, looking forward to hear your conclusions!
 

rnsc

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A lot of folks have gone in circles with this very thing especially regarding the Subaru oil bypass and flow rates. Ultimately I think you’ll be fine with whatever you decide. For myself my preference is OEM. If that’s unavailable or I’m feeling like grabbing something else I like the O’Reily’s MicroGard Select. Often a good deal with their oil+filter specials. Another consideration I don’t see often here are FULL filters. NAPA sells this brand. I haven’t tried them yet, but many folks running asian vehicles seem to like them.

Cheers!
Thanks for the new information, and I very much appreciate your many contributions to this thread. There are no O'Reily's in my part of the country, and I have never heard of FULL but will google them.

I will take this opportunity to express my twist on being "fine" since that is a common comment. Many things in life are like this: Everything degrades, wears out, dies, fails, eventually. Some of this is due to external factors (Which filter is used, whether you eat right), some are internal (Variations in the alloy or heat treating, your genetics). For this reason there are engines that will do fine for 300,000 miles with the cheapest crap oil and filter, and engines that fail with the best of the best. Short of a catastrophic failure (I put linseed oil in my engine and it froze up in less than an hour of highway driving, must have been the oil), it is impossible to know or even guess if it was the oil you have been putting in for the past 7 years or if there was a poor machining job on your crank shaft. But with some simple facts such as key oil performance characteristics under real world conditions and filter efficiency vs. particulate size, one can choose components that all other things being equal (And they never are equal) the engine will last longer. It skews your chances. You have the engine you have. How much money would it save you to have it to 6 months, 10,000 miles longer? I would say that would be worth about $1200-$1500. That would be about $30-50 per oil change. Or perhaps considerably more if you consider the disruption and HUGE cost of a sudden and serious failure earlier in the life of the vehicle such that it has to be fixed NOW. As one of the posters has said, oil and filters are cheap, timing chains and engines are expensive. I chose Amsoil about 20 years ago and have my own anecdotes that suggest that it was one of the best decisions I have made. I have been using their filters, but they are expensive, so I am digging to see if another might be for practical purposes just as good, not that any will cause my engine to literally blow up, but that the better filter will prolong the life of the engine and reduce the probability that it will be the factor that kills the car. I will never really know, but I hope to shift the curve. For me "Let it go" is to keep using Amsoil filters when I might get by for $30 per year less just fine. But I want to stay with the high end of "just fine", not a crap-shoot end. Those that tell me that this or that will be "Just fine" I respect also. They are likely right, and they have found their point of comfort. In fact the point of this thread was to try to put more concrete facts into the discussion so that the point of comfort was less subjective, more backed up by concrete data. I have not found that yet, but I have gotten additional good information, as well as links to MORE good information that I somehow have not seen before. I really don't want to buy another car. I want the one I have to be reliable for a long time. It is paid for, and they keep getting more expensive. Right now I pay about $70 per oil change (Gasp). $210 per year, 2100 over 10 years, 3150 over 15 in todays dollars, 5-7 percent of the price of a new car. Say I pay 2x what I could be spending: Will the extra I spend extend the life of the car 3-4%, in either miles or years? That would be about 6 months or 7500 miles. Not unreasonable... I have had mechanics for two vehicles come out to the service desk to tell me that the inside of my engine is in amazing condition for a vehicle with well over 100,000 miles on it. Coincidence? Maybe. Sounds pretty far-fetched to me. Both vehicles were traded in for other reasons, the engine still running like a top, but then that has been true of all of my vehicles.

I plan on posting my conclusions. I don't think they will be conclusive, but it looks like they will be helpful to me. Back to work!
 
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Thanks for the new information, and I very much appreciate your many contributions to this thread. There are no O'Reily's in my part of the country, and I have never heard of FULL but will google them.

I will take this opportunity to express my twist on being "fine" since that is a common comment. Many things in life are like this: Everything degrades, wears out, dies, fails, eventually. Some of this is due to external factors (Which filter is used, whether you eat right), some are internal (Variations in the alloy or heat treating, your genetics). For this reason there are engines that will do fine for 300,000 miles with the cheapest crap oil and filter, and engines that fail with the best of the best. Short of a catastrophic failure (I put linseed oil in my engine and it froze up in less than an hour of highway driving, must have been the oil), it is impossible to know or even guess if it was the oil you have been putting in for the past 7 years or if there was a poor machining job on your crank shaft. But with some simple facts such as key oil performance characteristics under real world conditions and filter efficiency vs. particulate size, one can choose components that all other things being equal (And they never are equal) the engine will last longer. It skews your chances. You have the engine you have. How much money would it save you to have it to 6 months, 10,000 miles longer? I would say that would be worth about $1200-$1500. That would be about $30-50 per oil change. Or perhaps considerably more if you consider the disruption and HUGE cost of a sudden and serious failure earlier in the life of the vehicle such that it has to be fixed NOW. As one of the posters has said, oil and filters are cheap, timing chains and engines are expensive. I chose Amsoil about 20 years ago and have my own anecdotes that suggest that it was one of the best decisions I have made. I have been using their filters, but they are expensive, so I am digging to see if another might be for practical purposes just as good, not that any will cause my engine to literally blow up, but that the better filter will prolong the life of the engine and reduce the probability that it will be the factor that kills the car. I will never really know, but I hope to shift the curve. For me "Let it go" is to keep using Amsoil filters when I might get by for $30 per year less just fine. But I want to stay with the high end of "just fine", not a crap-shoot end. Those that tell me that this or that will be "Just fine" I respect also. They are likely right, and they have found their point of comfort. In fact the point of this thread was to try to put more concrete facts into the discussion so that the point of comfort was less subjective, more backed up by concrete data. I have not found that yet, but I have gotten additional good information, as well as links to MORE good information that I somehow have not seen before. I really don't want to buy another car. I want the one I have to be reliable for a long time. It is paid for, and they keep getting more expensive. Right now I pay about $70 per oil change (Gasp). $210 per year, 2100 over 10 years, 3150 over 15 in todays dollars, 5-7 percent of the price of a new car. Say I pay 2x what I could be spending: Will the extra I spend extend the life of the car 3-4%, in either miles or years? That would be about 6 months or 7500 miles. Not unreasonable... I have had mechanics for two vehicles come out to the service desk to tell me that the inside of my engine is in amazing condition for a vehicle with well over 100,000 miles on it. Coincidence? Maybe. Sounds pretty far-fetched to me. Both vehicles were traded in for other reasons, the engine still running like a top, but then that has been true of all of my vehicles.

I plan on posting my conclusions. I don't think they will be conclusive, but it looks like they will be helpful to me. Back to work!

I would say if it's not broke don't fix it. Amsoil has billed itself as a unique automotive industry top tier oil and filter supplier. They are not without hiccups as seen in a recent thread here regarding causing an issue to a particular engine; however, I suspect many other filter brands would have been much slower to the punch to research, admit an issue, and correct (if at all). So in short, I think Amsoil is a great choice all the way around. If that's been working for you it's a solid choice.

I don't mean to be dismissive saying you'll be "just fine" using anything. I understand your goal is longevity of engine life. I think for most here the ultimate goal is the same. For me I just change my oil on the severe/special conditions change interval and generally just use OEM filters. Car manufacturers keep suppliers more accountable than auto part stores or individual consumers who can't afford a legal team. Quality Control tends to be taken more seriously for OEM inventory. Filters are shrink-wrapped and failures/defects are rarely seen. When there is a problem the supplier doesn't just get to ignore it or give the run-around. They correct or their lucrative OEM contract is at risk. For $6-$7/filter that's a nice perk and peace of mind added to the value of the product for me. It will be interesting to see if Subaru changes suppliers after this sudden inventory shortage of the current blue OEM filters.

Last, I know this is just a sample size of one and it's rather anecdotal: My first Subaru was a 1995 Legacy. I bought it around 2003 and it had 310,000 miles. The person I bought it from had done nothing but Grease Monkey and JiffyLube oil changes since he had bought it new with only the occasional trip to the dealer for things like timing belts and clutch replacement. He was religious about the maintenance schedule and had a record for each oil change every 3,000 miles. Did it consume oil? Yes, about 1 quart every 3,000 miles. Could that have been prevented with higher quality oil/filters? Maybe.. Maybe not, but if I had to guess it would probably be in better shape if it had been pampered with something like Amsoil products all those miles. I also assume had he used OEM filters (oil & air) it may have consumed less. We can't know though. I had that car until 410,000 miles and then was involved in an accident which totaled it. A sad day indeed, but it still had plenty of miles to give. They definitely made those engines well in 1995.

*edit*

Thinking of my old bullet-proof Subaru I'm reminded of this old craigslist ad: https://www.craigslist.org/about/best/hou/6565526716.html
😄
 
Last edited:
Joined
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Thanks for the new information, and I very much appreciate your many contributions to this thread. There are no O'Reily's in my part of the country, and I have never heard of FULL but will google them.

I will take this opportunity to express my twist on being "fine" since that is a common comment. Many things in life are like this: Everything degrades, wears out, dies, fails, eventually. Some of this is due to external factors (Which filter is used, whether you eat right), some are internal (Variations in the alloy or heat treating, your genetics). For this reason there are engines that will do fine for 300,000 miles with the cheapest crap oil and filter, and engines that fail with the best of the best. Short of a catastrophic failure (I put linseed oil in my engine and it froze up in less than an hour of highway driving, must have been the oil), it is impossible to know or even guess if it was the oil you have been putting in for the past 7 years or if there was a poor machining job on your crank shaft. But with some simple facts such as key oil performance characteristics under real world conditions and filter efficiency vs. particulate size, one can choose components that all other things being equal (And they never are equal) the engine will last longer. It skews your chances. You have the engine you have. How much money would it save you to have it to 6 months, 10,000 miles longer? I would say that would be worth about $1200-$1500. That would be about $30-50 per oil change. Or perhaps considerably more if you consider the disruption and HUGE cost of a sudden and serious failure earlier in the life of the vehicle such that it has to be fixed NOW. As one of the posters has said, oil and filters are cheap, timing chains and engines are expensive. I chose Amsoil about 20 years ago and have my own anecdotes that suggest that it was one of the best decisions I have made. I have been using their filters, but they are expensive, so I am digging to see if another might be for practical purposes just as good, not that any will cause my engine to literally blow up, but that the better filter will prolong the life of the engine and reduce the probability that it will be the factor that kills the car. I will never really know, but I hope to shift the curve. For me "Let it go" is to keep using Amsoil filters when I might get by for $30 per year less just fine. But I want to stay with the high end of "just fine", not a crap-shoot end. Those that tell me that this or that will be "Just fine" I respect also. They are likely right, and they have found their point of comfort. In fact the point of this thread was to try to put more concrete facts into the discussion so that the point of comfort was less subjective, more backed up by concrete data. I have not found that yet, but I have gotten additional good information, as well as links to MORE good information that I somehow have not seen before. I really don't want to buy another car. I want the one I have to be reliable for a long time. It is paid for, and they keep getting more expensive. Right now I pay about $70 per oil change (Gasp). $210 per year, 2100 over 10 years, 3150 over 15 in todays dollars, 5-7 percent of the price of a new car. Say I pay 2x what I could be spending: Will the extra I spend extend the life of the car 3-4%, in either miles or years? That would be about 6 months or 7500 miles. Not unreasonable... I have had mechanics for two vehicles come out to the service desk to tell me that the inside of my engine is in amazing condition for a vehicle with well over 100,000 miles on it. Coincidence? Maybe. Sounds pretty far-fetched to me. Both vehicles were traded in for other reasons, the engine still running like a top, but then that has been true of all of my vehicles.

I plan on posting my conclusions. I don't think they will be conclusive, but it looks like they will be helpful to me. Back to work!
Great post, and here’s another anecdotal point for you: my mail lady (rural route) has a ~’96 Legacy wagon with the 2.2. Around 2 years ago I asked her how many miles since she said she’s owned it since new. It was over 440k and the valve covers have never been off. I asked her maintenance schedule: full Amsoil all through the car including coolant, and Amsoil filters. The timing belt has been changed 5x along with water pump, and the car needed a radiator from rock damage. However, I don’t know if you can get more “severe service” than a rural route with dirt and gravel roads with all the start/stop. I’ll have to ask her again next time I see her, the car may be over 500k by now.

Caveat: I understand the EJ22 is different in some ways, better than the EJ25 and close to your new engine. But the majority of the engineering is likely almost identical. You certainly have a great thread going here even if the outcome comes down to OEM or the original Amsoil filter you are using!
 

rnsc

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Thanks! Busy with work this week, I hope to get back this weekend. Sorry about the gaps in attention.
 

rnsc

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I was hoping to improve the collective insight on this subject. While it has been a good conversation, I am afraid I only succeeded in deepening the questions that cannot be answered. This is a very complex system, far beyond the questions I raised, and our narrow, simplified view of the situation is simply ignorant. Even the principles and 'laws' that we learn in school are idealized and not applicable to real-world situations as I tried to think through. Without getting into details, I discussed this at length with someone who works to advance the accuracy of molecular modeling for a living. We haven't a clue how complicated this is. What is needed is the empirical data that none of us have access to. Comprehensive well designed and executed experiments are expensive, and likely even the filter manufacturers do not have the scope of data that we would like to see. They primarily need to be able to market some new 'innovation' or hype up some irrelavent characteristic such as the hole count and continue to whittle the cost to cater to those who buy solely on price, not come up with the best filter.

I don't think that we are in any better shape than when we started. Fundamentally the filter and engine manufacturers do not provide concrete empirical information regarding flow vs. pressure vs. viscosity and dirt load. Publishing what they have would only open them up to critique and would not be beneficial for them.

I have always used the Amsoil EAO filters, but they are expensive, but worse they were unobtainable for a long time. So I looked around and found WIX for 2-3x less money! Amsoil sold them before they made their own, and still sells them, so I took this as a recommendation. So I considered if they were suitable, and before long this thread was born.

I believe that I am going to blindly stick with the Amsoil filter because of personal experiences with the oil and several other products. I have decided to trust them. They seem to base their business on making money by making superior products, bought by people who are willing to pay a little more. I may very well be paying $8 more per oil change ($0.001 per mile, $300 more over the life of my Subaru) more than I have to. If this extends the life of the car by 4 weeks over 10-15 years, it will have paid for itself. But am I paying more for the right filter? Worst case I bought a good, competent product and will have wasted $300 in a well-intentioned attempt to extend a $35,000 investment. I am betting that I will do at least a little better than that, and being a long lever arm, I hope significantly better.

Out of appreciation for the effort and for completeness of the thread, I have responded below to the posts since my previous posting.

"Millions of people use them" and "I ran ABC filter for decades and my cars never blew up" miss the point. Damage due to poor lubrication is never instantly catastrophic. If it goes another oil change or two, any failure is not going to be associated with the oil used a couple of changes ago. We all expect our engine to wear out eventually. If a wrist pin bearing goes at 187,000 miles, do we blame the oil we used? No, we just figure it wore out and it is time to buy a new car. Yet the oil, filter, and our oil change interval may have contributed to more wear per mile than would have occurred if the engine had been lubricated better. I would be willing to bet that if you replaced the filter with an empty can and changed your oil per the manufacturer's schedule, or even half as often, that the majority of the time the engine would get to the end of the warranty without a failure. Depending on the warranty length, oil change interval, and the price of the filters you don't buy, you would save a small few hundred dollars. But engines and cars are expensive, so I am trying to skew the odds in my favor. For me, if I extend the life of the car by a month I will have likely paid for all of the better filters, and if I extend it a few months, for the better oil too. Everyone has to make their own decisions based on their own set of incomplete information and personal intuition. I have decided that quality is a big lever on the rate of engine wear.

'Supply chain' issues for many filters: If we could not get ANY filter, we would be in big trouble. I will keep a stock in my garage, and a list of second-choice filters.

ZeeOSix in post #3, I am quite sure that we agree in our understanding, however it may have appeared from my words.

ZeeOSix: Absolutely, the curve is only one data point, but it is one data point of the missing information. And one is infinitely more than zero! If we had a family of curves vs. measured viscosity that would be awesome, then we could take our favorite oil at different weights and temperatures and see how the filter behaved at that point. Regarding "If you're worried about the filter bypassing too much on a high pump flowing Subaru, then use filters with the high bypass setting specified by Subaru." I will address this later, but I have not seen a filter with the Subaru bypass valve pressure. For now because there are two branches to the conversation I will overlook this and address your statement as though there were such a filter... Continuing: Yes but if it is set too high, that will leave less pressure to push enough oil through the engine. If we never go above 6000 PSI (Which would probably be wise) evidently the positive displacement pump moves 58.1 qt/m presumably out through the engine, and even more than that actually pumped but bypassed inside the pump because the output pressure of 46.8 PSI exceeds the 21.7 PSI of the first stage internal shunt/relief valve which MUST be open in this situation. But all we need to know is that it is moving 58.1 qt/min externally. Nominally 23.2 PSI of the pump output pressure is dropped across the filter (Like your resistor to use the electrical analogy), leaving 23.6 PSI to move that oil through the engine. Though not stated, what external "load" could be more appropriate for this experiment other than the intended engine, and FB25?

So if the WIX opens at 27 PSI that is about 4 PSI higher, leaving only 19.6 to push oil through the engine. But the irresistable flow determines the pressure with a positive displacement pump, not the other way around. More oil will be shunted inside the pump because of the higher output pressure forced by the 27PSI filter bypass valve, so the engine will get less oil. Is this OK? Geez, I don't know! If the engine with the Subaru filter has an overwhelming greater amount of oil than is needed, it is probably fine. If it is marginal under some conditions, it will not be fine under that condition. I do not know how the relief channel for the 21.7 PSI first stage flow rate will vary vs. a 16% increase in pressure, but it will be more, but probably not proportionately more.

As many have stated, there has been discussion along these lines before. In one of those threads someone stated that engines are never starved for oil at high RPM, starvation only occurs at very low RPM. This would be very interesting to explore. If the engine is developing more torque at the high RPM (What RPM is the peak of an FB25 torque curve?) then there may be more radial (lateral?) load on the bearing, requiring MORE pressure to maintain the film. We need a bearing expert. Some of the bearings are throwing pistons back and forth and the forces must get enormous (Probably why wrist pin bearings go!) It gets very complicated very quickly.

I see the superficial argument that a higher filter relief valve pressure is good in that it avoids having the filter dump dirt into the engine as frequently (as my original note projected to happen in the 3xxx RPM range), but it is not that simple. And metal on metal would be catastrophically worse than a little dirt. Again, lack of knowledge about how much of that 58.1 qt/min oil flow the engine really needs at 6000 RPM.

Getting back to ZeeOSix' graph of PSI vs. GPM for a Purolator PureOne which has synthetic blend media, this is the closest thing we have to a fact. Is this is representative of all synthetic blend media? How is completely synthetic different? How is all cellulous different? How is it different for different viscosities, like 0W20 or 5W30 at 0 or 10 or 20F? The answer easy directionally, but how much, and with what shape curve? We don't know, but at LEAST we see that for this case, and likely a clean filter and clean oil, the pressure is really quite low. The highest rate we talk about is about 60qt/min which incurs a 7 PSI pressure drop. It would not be hard to imagine that a little dirt in the filter and cold oil would have dramatically more resistance than a brand new clean filter and oil, opening the relief valve. Similarly it seems to be common knowledge that synthetic blend filters require much less pressure. Fram Tough Guard are marketed as being "synthetic blend" too. WIX 57055 is marketed as having "Enhanced Cellulous" media (whatever that means). Does that mean it requires more pressure? And paper is what synthetic is less than, so it must be more.

Brian533, my mistake! Good catch, thank you. The pressure is 5.8 PSI at 600 RPM, NOT 40 PSI, I read the wrong number off of the table. 600RPM pumps 6.1 US qt/min at 5.8 PSI so the valve will be closed. The Purolater PureOne at 200 F and 5W30 per the graph ZeeOSix provided will drop 2.3 PSI, leaving 2.8 PSI to force oil through the engine. Evidently that is enough or it would be higher. We really can't go anywhere with this because we (I) don't know how pressure varies vs. flow through either the filter or the engine. The positive displacement pump insists on driving that 6.1 qts: That is the independent variable. The 5.8 PSI is NOT a characteristic of the pump at 600 RPM, rather it is the outcome of *whatever it takes* to move that 6.1 qt/min through the engine. It happens to take (evidently) 2.8 PSI! And the engine DOES get 6.1 sq/min. So no, the pump bypass valve does NOT open, nor does the filter relief valve.

The 6000 RPM data I quoted was correct: 6000 RPM, 48.4 qt/min, at 46.8 PSI. Recognize that these are the pump specifications as a black box: Whether or not an internal bypass in the pump opens is immaterial: At the given RPM it moves this much oil OUT of the pump if this is the back-pressure. If the back-pressure is lower or higher, less or more will go through the internal pump bypass. That back-pressure and the resistance of the filter+engine determines how much oil takes that route, the rest will go through the pumps internal bypass (The qt/min number). The two routes (pump bypass vs. filter+engine) will find a balance based on their respective resistance to the oil flow. Whether or not the filter relief valve opened is immaterial to *these* numbers.

On the other hand, as a system we care what the pressure is because if it is above the filter relief valve pressure it opens and alot of dirt is flushed out of the filter and through the engine. There has to be some context for these specifications, and the stated "load" on the pump is a specific oil filter which we can safely assume is the Subaru filter. The only specifications that matter are the by-pass valve opening pressure which they give, and the pressure vs. viscosity and flow 3-D graph, which they do not provide. But we can say that for the 600 RPM case, the valve does not open, otherwise the discharge pressure of the pump would be something north of 23.2 PSI. For the 6000 RPM case we cannot know whether or not the valve opens because we don't know the pressure drop through the engine or the pressure drop through the filter (One of these would do since the total is given in the FSM as 46.8PSI).

WPod: Yes, the oil filter bypass valve opens at 23.2 PSI. The alternative route (That I was not talking about) are the bypass valves internal to the pump at 21.7 PSI and 82.6 PSI. I agree with your explanation of what is happening. Nobody makes a filter that is "proper rated" except for Subaru (Which is "proper rated" by definition vs. by specification because the filter is incompletely specified). When I use the Subaru filter with 0W20 oil the engine rattles alarmingly for a very small number of seconds then quieter until I drive it a several hundred feet. The Amsoil filter does not do this, it rattles for some fraction of a second and quiets down much more quickly after that. Using 5W30 seems to be markedly better with either filter, but follows the same pattern (Noisy with the Sube filter, much quieter with the Amsoil. I wish I had better records to quote, but that is the gist of it. The devil of it is that my son has a 2017 forester with the same engine that does exactly the opposite (!). There are also people on both sides of the fence on this topic on various forums with respect to the Subaru filter. What a zoo. When my engine sounds like there is a handfull of bolts rattling around under the valve cover for a couple of seconds then trails off, it is hard to be happy. Whatever else is true, that cannot be a positive thing. For me, the "easy button" of just using the Subaru filter is cringe-worthy.

ZeeOSix: I emailed WIX twice. They did not respond to either email. Regarding viscosity, I have been using Amsoil oil for twenty years. Whenever it gets cold oil had always been visibly thicker - until I started using Amsoil. I am sure that it is thicker when I change my oil on a frozen driveway when the oil has been in the unheated garage, but since I have been using Amsoil, not noticeably. And the vehicles don't crank much if any slower either. Is it that cars are different than they used to be? I supposed that may be part of it, but the oil has to be part of that too.

SubieRubyRoo, What do you base your statement on that the 57055 with a 27 PSI bypass meets the Subaru FB25 requirements? The Subaru FSM specifies a filter with 23.2 PSI, not 27. The WIX filter does NOT meet that Subaru spec. If that is an indication that the WIX filter requires more pressure than the Subaru filter to force a given volume of oil through, that means that at any given RPM there will be about 16% *less* pressure available to force oil through the engine until the bypass valve opens at 27 PSI. Once the total pressure is above 21.7 (Above about 21.7/5.8)*600 = 2244 RPM) the pump internal shunt is siphoning off some of the volume so the engine sees less volume to boot. Only some unknown fraction, presumably not a ton less. But less.

It is not my intent to continue this thread unless there is new and substantial information. If something is added that leads to a more concrete, fact-based analysis, that would be great.

Thank you again.
 

ZeeOSix

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I'll start off just saying I think you are over thinking this stuff and getting tangled up in the weeds. If you haven't read this entire thread linked below, I highly suggest that you do. The ISO 4548 test standard was invented over 20 years ago for a good reason - to give a standardized test procedure and metrics to determine the performance of oil filters over a wide range areas.

This link jumps to the resulting data, but it might be good to read this thread from Post #1 too.

ZeeOSix in post #3, I am quite sure that we agree in our understanding, however it may have appeared from my words.

ZeeOSix: Absolutely, the curve is only one data point, but it is one data point of the missing information. And one is infinitely more than zero! If we had a family of curves vs. measured viscosity that would be awesome, then we could take our favorite oil at different weights and temperatures and see how the filter behaved at that point. Regarding "If you're worried about the filter bypassing too much on a high pump flowing Subaru, then use filters with the high bypass setting specified by Subaru."
Getting back to ZeeOSix' graph of PSI vs. GPM for a Purolator PureOne which has synthetic blend media, this is the closest thing we have to a fact. Is this is representative of all synthetic blend media? How is completely synthetic different? How is all cellulous different? How is it different for different viscosities, like 0W20 or 5W30 at 0 or 10 or 20F? The answer easy directionally, but how much, and with what shape curve? We don't know, but at LEAST we see that for this case, and likely a clean filter and clean oil, the pressure is really quite low. The highest rate we talk about is about 60qt/min which incurs a 7 PSI pressure drop. It would not be hard to imagine that a little dirt in the filter and cold oil would have dramatically more resistance than a brand new clean filter and oil, opening the relief valve. Similarly it seems to be common knowledge that synthetic blend filters require much less pressure. Fram Tough Guard are marketed as being "synthetic blend" too. WIX 57055 is marketed as having "Enhanced Cellulous" media (whatever that means). Does that mean it requires more pressure? And paper is what synthetic is less than, so it must be more.
The oil filter "Delta-p vs Flow" curve is going to be dependent on these main 3 factors: 1) Flow resistance of the filter assembly, 2) oil viscosity and 3) oil flow rate. Yes, the whole curve will shift up or down depending on the oil viscosity (other factors held constant). Obviously the whole curve will shift up on the Y-axis as oil viscosity is increased. The curve will shift down as the viscosity decreases. That gives a "family of curves" on the PSID (aka "delta-p") vs flow rate graph.

The flow resistance of the filter assembly (item 1 above) is comprised of the separate delta-p drops across all the elements of the filter. The media is the largest contributor to the assembly delta-p. The base plate holes, the center tube holes/louvers/eCore cage are only a small part of the total delta-p across the assembly. Obviously, the design of the media itself has a PSID flow resistance vs flow curve for each square inch of media ... so keep in mind that the total delta-p across the entire media element is also dependent on the total area of the media. That's one reason that the PureOne that I posted the PSID vs Flow graph for has pretty low flow resistance even though it's not a full synthetic media ... because the PureOne filters have a lot of total media area.

An oil filter designer is going to design the filter to have an acceptable PDIS vs Flow curve across the entire filter assembly - including the media design, the total media area, and the inlet and center tube holes/louvers/eCore cage. The graphs in the thread link at the top of this post shows that all of those tested filters have pretty close PSID vs Flow curves. When the oil is at full operating temperature, all oil filters (when new of course) will all have a delta-p that is +/- a few PSI of each other. It can differ more when the oil is very thick and cold, but again that's what a filter bypass valve setting is for. And also, that's what low engine revs are for too when the oil is cold ... to help keep the delta-p across the filter lower so the bypass valve stays closed. High revs with very cold oil is most likely going to put any oil filter into bypass to some degree.

Also, all you can do is trust the filter designers who specify an oil filter for vehicles to know what filter bypass setting is going to work. One reason Subaru oil filters typically have a higher bypass valve setting is because of the high flow PD oil pumps (got a PD pump in there, lol) used in some engines. Also, keep in mind that the filter bypass valve setting is dependent on the filter's total flow resistance and delta-p performance. A filter that has a little more flow delta-p may have the bypass valve setting a bit higher to account for that too. Total expected filter debris loading (which increases fiiler delta-p over the OCI) is also a consideration in the bypass valve setting. Lots of factors going on.

ZeeOSix: I emailed WIX twice. They did not respond to either email. Regarding viscosity, I have been using Amsoil oil for twenty years. Whenever it gets cold oil had always been visibly thicker - until I started using Amsoil. I am sure that it is thicker when I change my oil on a frozen driveway when the oil has been in the unheated garage, but since I have been using Amsoil, not noticeably. And the vehicles don't crank much if any slower either. Is it that cars are different than they used to be? I supposed that may be part of it, but the oil has to be part of that too.
If you ever hang out in the PCMO forum there are lots of discussions about the "W" (Winder/cold starting) rating of oil, the Cold Cranking viscosity and MRV (Pumpability) viscosity tests used to come up with the SAE J300 "W" (Winter) grade of oils. The "W" rating is a grade, which means the actual viscosity of 10 different brand oils could be somewhat different at the same test temperature, and still fall into the same W rating (ie, they would all fall into the "5W" grade rating for example). That means it's entirely possible for one 5W rated oil to make the engine crank over a little faster or slower than another 5W rated oil.

Anyway, the important thing about the SAE J300 "W" rating of oil is to use one that is applicable and recommended by the engine maker to the climate conditions the car is used for. And don't rev the engine too high until the oil warms up ... that also keeps the delta-p (there's the delta-p again, lol) lower across the filter and helps keep the filter bypass valve from opening.
 
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I was hoping to improve the collective insight on this subject. While it has been a good conversation, I am afraid I only succeeded in deepening the questions that cannot be answered. This is a very complex system, far beyond the questions I raised, and our narrow, simplified view of the situation is simply ignorant. Even the principles and 'laws' that we learn in school are idealized and not applicable to real-world situations as I tried to think through. Without getting into details, I discussed this at length with someone who works to advance the accuracy of molecular modeling for a living. We haven't a clue how complicated this is. What is needed is the empirical data that none of us have access to. Comprehensive well designed and executed experiments are expensive, and likely even the filter manufacturers do not have the scope of data that we would like to see. They primarily need to be able to market some new 'innovation' or hype up some irrelavent characteristic such as the hole count and continue to whittle the cost to cater to those who buy solely on price, not come up with the best filter.

I don't think that we are in any better shape than when we started. Fundamentally the filter and engine manufacturers do not provide concrete empirical information regarding flow vs. pressure vs. viscosity and dirt load. Publishing what they have would only open them up to critique and would not be beneficial for them.

I have always used the Amsoil EAO filters, but they are expensive, but worse they were unobtainable for a long time. So I looked around and found WIX for 2-3x less money! Amsoil sold them before they made their own, and still sells them, so I took this as a recommendation. So I considered if they were suitable, and before long this thread was born.

I believe that I am going to blindly stick with the Amsoil filter because of personal experiences with the oil and several other products. I have decided to trust them. They seem to base their business on making money by making superior products, bought by people who are willing to pay a little more. I may very well be paying $8 more per oil change ($0.001 per mile, $300 more over the life of my Subaru) more than I have to. If this extends the life of the car by 4 weeks over 10-15 years, it will have paid for itself. But am I paying more for the right filter? Worst case I bought a good, competent product and will have wasted $300 in a well-intentioned attempt to extend a $35,000 investment. I am betting that I will do at least a little better than that, and being a long lever arm, I hope significantly better.

Out of appreciation for the effort and for completeness of the thread, I have responded below to the posts since my previous posting.

"Millions of people use them" and "I ran ABC filter for decades and my cars never blew up" miss the point. Damage due to poor lubrication is never instantly catastrophic. If it goes another oil change or two, any failure is not going to be associated with the oil used a couple of changes ago. We all expect our engine to wear out eventually. If a wrist pin bearing goes at 187,000 miles, do we blame the oil we used? No, we just figure it wore out and it is time to buy a new car. Yet the oil, filter, and our oil change interval may have contributed to more wear per mile than would have occurred if the engine had been lubricated better. I would be willing to bet that if you replaced the filter with an empty can and changed your oil per the manufacturer's schedule, or even half as often, that the majority of the time the engine would get to the end of the warranty without a failure. Depending on the warranty length, oil change interval, and the price of the filters you don't buy, you would save a small few hundred dollars. But engines and cars are expensive, so I am trying to skew the odds in my favor. For me, if I extend the life of the car by a month I will have likely paid for all of the better filters, and if I extend it a few months, for the better oil too. Everyone has to make their own decisions based on their own set of incomplete information and personal intuition. I have decided that quality is a big lever on the rate of engine wear.

'Supply chain' issues for many filters: If we could not get ANY filter, we would be in big trouble. I will keep a stock in my garage, and a list of second-choice filters.

ZeeOSix in post #3, I am quite sure that we agree in our understanding, however it may have appeared from my words.

ZeeOSix: Absolutely, the curve is only one data point, but it is one data point of the missing information. And one is infinitely more than zero! If we had a family of curves vs. measured viscosity that would be awesome, then we could take our favorite oil at different weights and temperatures and see how the filter behaved at that point. Regarding "If you're worried about the filter bypassing too much on a high pump flowing Subaru, then use filters with the high bypass setting specified by Subaru." I will address this later, but I have not seen a filter with the Subaru bypass valve pressure. For now because there are two branches to the conversation I will overlook this and address your statement as though there were such a filter... Continuing: Yes but if it is set too high, that will leave less pressure to push enough oil through the engine. If we never go above 6000 PSI (Which would probably be wise) evidently the positive displacement pump moves 58.1 qt/m presumably out through the engine, and even more than that actually pumped but bypassed inside the pump because the output pressure of 46.8 PSI exceeds the 21.7 PSI of the first stage internal shunt/relief valve which MUST be open in this situation. But all we need to know is that it is moving 58.1 qt/min externally. Nominally 23.2 PSI of the pump output pressure is dropped across the filter (Like your resistor to use the electrical analogy), leaving 23.6 PSI to move that oil through the engine. Though not stated, what external "load" could be more appropriate for this experiment other than the intended engine, and FB25?

So if the WIX opens at 27 PSI that is about 4 PSI higher, leaving only 19.6 to push oil through the engine. But the irresistable flow determines the pressure with a positive displacement pump, not the other way around. More oil will be shunted inside the pump because of the higher output pressure forced by the 27PSI filter bypass valve, so the engine will get less oil. Is this OK? Geez, I don't know! If the engine with the Subaru filter has an overwhelming greater amount of oil than is needed, it is probably fine. If it is marginal under some conditions, it will not be fine under that condition. I do not know how the relief channel for the 21.7 PSI first stage flow rate will vary vs. a 16% increase in pressure, but it will be more, but probably not proportionately more.

As many have stated, there has been discussion along these lines before. In one of those threads someone stated that engines are never starved for oil at high RPM, starvation only occurs at very low RPM. This would be very interesting to explore. If the engine is developing more torque at the high RPM (What RPM is the peak of an FB25 torque curve?) then there may be more radial (lateral?) load on the bearing, requiring MORE pressure to maintain the film. We need a bearing expert. Some of the bearings are throwing pistons back and forth and the forces must get enormous (Probably why wrist pin bearings go!) It gets very complicated very quickly.

I see the superficial argument that a higher filter relief valve pressure is good in that it avoids having the filter dump dirt into the engine as frequently (as my original note projected to happen in the 3xxx RPM range), but it is not that simple. And metal on metal would be catastrophically worse than a little dirt. Again, lack of knowledge about how much of that 58.1 qt/min oil flow the engine really needs at 6000 RPM.

Getting back to ZeeOSix' graph of PSI vs. GPM for a Purolator PureOne which has synthetic blend media, this is the closest thing we have to a fact. Is this is representative of all synthetic blend media? How is completely synthetic different? How is all cellulous different? How is it different for different viscosities, like 0W20 or 5W30 at 0 or 10 or 20F? The answer easy directionally, but how much, and with what shape curve? We don't know, but at LEAST we see that for this case, and likely a clean filter and clean oil, the pressure is really quite low. The highest rate we talk about is about 60qt/min which incurs a 7 PSI pressure drop. It would not be hard to imagine that a little dirt in the filter and cold oil would have dramatically more resistance than a brand new clean filter and oil, opening the relief valve. Similarly it seems to be common knowledge that synthetic blend filters require much less pressure. Fram Tough Guard are marketed as being "synthetic blend" too. WIX 57055 is marketed as having "Enhanced Cellulous" media (whatever that means). Does that mean it requires more pressure? And paper is what synthetic is less than, so it must be more.

Brian533, my mistake! Good catch, thank you. The pressure is 5.8 PSI at 600 RPM, NOT 40 PSI, I read the wrong number off of the table. 600RPM pumps 6.1 US qt/min at 5.8 PSI so the valve will be closed. The Purolater PureOne at 200 F and 5W30 per the graph ZeeOSix provided will drop 2.3 PSI, leaving 2.8 PSI to force oil through the engine. Evidently that is enough or it would be higher. We really can't go anywhere with this because we (I) don't know how pressure varies vs. flow through either the filter or the engine. The positive displacement pump insists on driving that 6.1 qts: That is the independent variable. The 5.8 PSI is NOT a characteristic of the pump at 600 RPM, rather it is the outcome of *whatever it takes* to move that 6.1 qt/min through the engine. It happens to take (evidently) 2.8 PSI! And the engine DOES get 6.1 sq/min. So no, the pump bypass valve does NOT open, nor does the filter relief valve.

The 6000 RPM data I quoted was correct: 6000 RPM, 48.4 qt/min, at 46.8 PSI. Recognize that these are the pump specifications as a black box: Whether or not an internal bypass in the pump opens is immaterial: At the given RPM it moves this much oil OUT of the pump if this is the back-pressure. If the back-pressure is lower or higher, less or more will go through the internal pump bypass. That back-pressure and the resistance of the filter+engine determines how much oil takes that route, the rest will go through the pumps internal bypass (The qt/min number). The two routes (pump bypass vs. filter+engine) will find a balance based on their respective resistance to the oil flow. Whether or not the filter relief valve opened is immaterial to *these* numbers.

On the other hand, as a system we care what the pressure is because if it is above the filter relief valve pressure it opens and alot of dirt is flushed out of the filter and through the engine. There has to be some context for these specifications, and the stated "load" on the pump is a specific oil filter which we can safely assume is the Subaru filter. The only specifications that matter are the by-pass valve opening pressure which they give, and the pressure vs. viscosity and flow 3-D graph, which they do not provide. But we can say that for the 600 RPM case, the valve does not open, otherwise the discharge pressure of the pump would be something north of 23.2 PSI. For the 6000 RPM case we cannot know whether or not the valve opens because we don't know the pressure drop through the engine or the pressure drop through the filter (One of these would do since the total is given in the FSM as 46.8PSI).

WPod: Yes, the oil filter bypass valve opens at 23.2 PSI. The alternative route (That I was not talking about) are the bypass valves internal to the pump at 21.7 PSI and 82.6 PSI. I agree with your explanation of what is happening. Nobody makes a filter that is "proper rated" except for Subaru (Which is "proper rated" by definition vs. by specification because the filter is incompletely specified). When I use the Subaru filter with 0W20 oil the engine rattles alarmingly for a very small number of seconds then quieter until I drive it a several hundred feet. The Amsoil filter does not do this, it rattles for some fraction of a second and quiets down much more quickly after that. Using 5W30 seems to be markedly better with either filter, but follows the same pattern (Noisy with the Sube filter, much quieter with the Amsoil. I wish I had better records to quote, but that is the gist of it. The devil of it is that my son has a 2017 forester with the same engine that does exactly the opposite (!). There are also people on both sides of the fence on this topic on various forums with respect to the Subaru filter. What a zoo. When my engine sounds like there is a handfull of bolts rattling around under the valve cover for a couple of seconds then trails off, it is hard to be happy. Whatever else is true, that cannot be a positive thing. For me, the "easy button" of just using the Subaru filter is cringe-worthy.

ZeeOSix: I emailed WIX twice. They did not respond to either email. Regarding viscosity, I have been using Amsoil oil for twenty years. Whenever it gets cold oil had always been visibly thicker - until I started using Amsoil. I am sure that it is thicker when I change my oil on a frozen driveway when the oil has been in the unheated garage, but since I have been using Amsoil, not noticeably. And the vehicles don't crank much if any slower either. Is it that cars are different than they used to be? I supposed that may be part of it, but the oil has to be part of that too.

SubieRubyRoo, What do you base your statement on that the 57055 with a 27 PSI bypass meets the Subaru FB25 requirements? The Subaru FSM specifies a filter with 23.2 PSI, not 27. The WIX filter does NOT meet that Subaru spec. If that is an indication that the WIX filter requires more pressure than the Subaru filter to force a given volume of oil through, that means that at any given RPM there will be about 16% *less* pressure available to force oil through the engine until the bypass valve opens at 27 PSI. Once the total pressure is above 21.7 (Above about 21.7/5.8)*600 = 2244 RPM) the pump internal shunt is siphoning off some of the volume so the engine sees less volume to boot. Only some unknown fraction, presumably not a ton less. But less.

It is not my intent to continue this thread unless there is new and substantial information. If something is added that leads to a more concrete, fact-based analysis, that would be great.

Thank you again.
Pressure inside of an oil filter does not work the way you assume it does. You’re misconstruing delta psi across the element with flow. When a filter bypass opens, pressure from the pump does not disappear from the element and magically find its way only through the bypass.

And yes, you’re way overthinking this, and the above misconceptions feed your apparent conundrum.
 

twX

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I haven't read this whole thread, but I'll give a summary of my own findings with respect to finding an "ideal" oil filter for my 2015 Subaru WRX.

The bypass pressure itself is not so relevant. What is important is the oil flow rate at which the filter starts bypassing. This depends on the bypass pressure setting, and on the filter restriction to flow. A filter with a 12 psi bypass would start bypassing at the same flow rate as a filter with a 23 psi bypass, if the 12 psi filter had around 30% less flow restriction of the 23 psi filter. (The relationship between flow and pressure is not linear.)

In other words, a 12 psi bypass filter that is around 45% larger (more media area), would bypass at the same flow as a smaller filter with a 23 psi bypass, all else being equal. Unfortunately, there are not many options for oversized/high flow filters with a low micron rating and an M20x1.5 thread. I use a FRAM Ultra XG3593A, which is around 10% larger than the recommended XG9688. I have no proof that it flows better, but it is larger and is the same filter recommended for another car of mine, the Acura Integra GS-R, which also has a high flow oil pump (71 L/min.)

The FRAM Ultra also flows better than most other filters tested in the Ascent Filtration test you can find on this forum. Based on the pressure differential tests in that comparison, I suspect that the FRAM filter on my Subaru will still start bypassing above 4500 rpm or so, even with warm oil, and might bypass 20% of oil flow near redline. At cold startup and during engine warmup, it will be bypassing even at idle or cruising revs (as will the Subaru filter).

So, what's more important? Preventing the filter from bypassing as much and as often? Or better filtration efficiency? I believe filtration efficiency is much more important. A low-micron filter like the FRAM Ultra will capture particles in the under 20 micron range at a rate of over 100 times that of a 40-50 micron filter. Even if the low-micron filter is bypassing 20% of oil flow, it will still be more efficient than a high-micron filter that is not bypassing at all, for particles smaller than 23 micron or so. Most engine wear is caused by particles in the 2 to 30 micron range. Keep in mind also that the low-micron filter will be flowing cleaner oil from the sump, and most of the time it will not be bypassing at all.
 

ZeeOSix

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The bypass pressure itself is not so relevant. What is important is the oil flow rate at which the filter starts bypassing. This depends on the bypass pressure setting, and on the filter restriction to flow. A filter with a 12 psi bypass would start bypassing at the same flow rate as a filter with a 23 psi bypass, if the 12 psi filter had around 30% less flow restriction of the 23 psi filter. (The relationship between flow and pressure is not linear.)
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The FRAM Ultra also flows better than most other filters tested in the Ascent Filtration test you can find on this forum. Based on the pressure differential tests in that comparison, I suspect that the FRAM filter on my Subaru will still start bypassing above 4500 rpm or so, even with warm oil, and might bypass 20% of oil flow near redline. At cold startup and during engine warmup, it will be bypassing even at idle or cruising revs (as will the Subaru filter).
True that for a given media design that more media area results in less delta-p with all other factors held constant. Your assumed numbers could only be proven in a controlled bench test. One thing is for sure, regardless of the filter and it's bypass setting, it's always a good idea to not go gonzo with high engine RPM until the oil if near fully warmed up.

This graph from post #4 shows that the PureOne (medium sized model) could flow way past the GPM output of even the crazy Subaru engines before hitting it's bypass setting. At 12 GPM, the delta-p was only 5 PSI. Keep in mind this is on a new filter and with the oil viscosity basically what a 5W-30 would be at 200 deg F.

1668920398574-jpg.127055
 
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