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

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WIX filter vs. Subaru Oil Pump/Filter Compatibility analysis

This is a long post that attempts to draw concrete conclusions about the
suitability of the WIX 57055 filter in a Subaru FB engine based on
pressures and flow rates published in the FB service manual and 57055
specifications on the WIX web site. Based on this analysis the 57055 is
clearly not suitable for use in an FB engine, the only apparent fly in
the ointment being that WIX does not communicate what they mean when
they say that the 57055 has a maximum flow rate of 8-10 GPM. I have no choice but to accept that statement at face value.

It is certainly also true that this is not my field of expertise,
however this is just math, so the conclusion is inescapable UNLESS
there is something wrong with my understanding, or or my analysis (which
are not unlikely) or if WIX was just kidding when they stated that the
maximum flow through the 57055 is 8-10 GPM. I assume that given an
explanation of what they mean by "max flow" would help make sense of
it all.

I hope that some of you can shed some light, and that WIX might even
pipe up and explain what they mean by max flow, making this analysis
whole and telling me if I should use the 57055 filter in my FB.

If it seems worthwhile to move this topic from opinions to facts,
please read on and comment - please correct me and add information
so that we *all* can have solid ground to stand on. Thank you!

The oil pump moves a certain volume of oil per revolution regardless of back pressure, or something has to give (whatever that means). To deal with this situation there is a relief valve at a certain pressure inside the pump. Therefore the pump moves that amount of oil and the pressure increases proportional to engine speed to overcome whatever resistance to flow that there is until the valve opens.

When the valve opens, whatever that pressure pushes through the filter and engine flows through the engine, the rest goes through the relief valve and recirculates internal to the pump. This caps the pressure available to push oil through the engine, and less oil flows through the engine than the pump pumps. Presumably at this high pressure, high flow situation, there is plenty of oil flow through the engine.

The oil pump internal relief valve pressure less the oil filter bypass valve pressure is what is available to push oil through the engine at minimum. If the oil flows through the filter media easily and the filter bypass valve does not open (Which we hope it does not!) then there is more pressure to push oil through the engine.

Now for the problems when evaluating whether to use a Subaru or a WIX filter (or anything else for which complete specifications are available!).

The FSM (2016 Outback FB25) states that the oil pump discharges 6.1 US qt/m at 40 PSI at 600 RPM, and 58.1 US qt/m at 46.8 PSI at 6000 RPM. This higher RPM case is the stress case.

The relief valve in the Subaru pump has two steps: The first step is 21.7 PSI (Just under the 23.2 PSI of the oil filter). I assume that this is only a limited, restricted bypass otherwise the main relief valve would never open. This will result in a designed lesser flow out of the pump and through the media and engine, and so that back pressure will grow more slowly as RPM increases further, avoiding having the main relief valve open. In effect it says that there is plenty of oil flowing through the engine at this high RPM, and it cuts down on how fast the pressure is growing with RPM to avoid opening the filter bypass valve during normal operating conditions with a clean enough filter. In effect it make the pump behave like it has a smaller displacement. Good idea.

The WIX filter bypass valve opens at 27 PSI. This would give more margin for tolerances to ensure that the filter bypass valve (Not talked about yet) doesn't open at almost the same time that the first level relief valve opens, the lower apparent pump volume per revolution resulting in the flow that will create enough pressure to open the filter bypass value arriving at a higher RPM. So much the better as long as there is enough pressure left to force oil through the engine and that the resulting lower flow per RPM is sufficient! I read that oil required to lubricate is proportional to engine RPM so this does concern me, but it must be that there is more oil flowing than is needed or they would not have done this.

Given that the pump's main relief valve opens at 82.6 PSI, the difference between the 23.2 PSI pressure drop of Subaru's filter which leaves 59.4 PSI to push oil through the engine and WIX' 27 PSI pressure drop which leaves 55.6 PSI to push oil through the engine in the most extreme condition is likely not significant. Surely the design has more operating margin that the difference between 59 and 56 PSI (Not that we should eat into their design margins, but this doesn't sound like a big deal).

Everything sounds good so far. Notice that at 6000 RPM (Redline) the pump wants to move 58.1 US qts per minute through the filter, and will generate 46.8 PSI to do that. This specification has to be under some well defined conditions, which must be with a Subaru filter in an FB25. There are two possibilities that could be happening here:

(1) The Subaru filter passes the 58.1 qts per minute through the filter without building up to the 23.2 PSI bypass valve pressure, leaving some majority greater than 23.6 PSI of the 46.8 PSI developed to push oil through the engine (Although this analysis is in the context of the Subaru filter specification from the FSM, this would be even more likely to be the case with a synthetic media filter that is always talked about as requiring much less pressure to force the oil through).

(2) The bypass valve opened at 23.2 PSI, and the engine back pressure resulting from the oil viscosity must be 23.6 PSI. This would mean that the Subaru filter bypass valve is open over a portion of the 0-6000 RPM range, dropping 23.2 PSI through the valve and leaving 23.6 PSI to push oil through the engine. In other words, every time someone revs the engine over some RPM that is less than the 6000 RPM redline, the bypass valve opens flushing dirty oil through the engine! This is not desirable.

Now for the hard question. The WIX 57055 Product Specifications from the WIX web site specifies "Max Flow Rate" of "8-10 GPM", that is 32-40 US qt per minute. Yet at 6000 RPM the FB25 oil pump IS pushing out 58.1 qts per minute (At 46.8 PSI).

This comes down to the question of what "Max Flow Rate" means. Does the media magically allow 32-40 qts per minute through but not a drop more? I suspect that the pressure vs. forced flow curve is an exponentially increasing curve. Wanting a single number for the specification, somebody said "Gee, between 32 and 40 qts per minute it goes up sharply." Or perhaps the 8-10 GPM rate is a commonly used flow for measuring pressure in the oil filter industry, or at a pressure that is the highest that the media can withstand before rupture. WIX does not tell us what that specification means, making it frustratingly meaningless. Whatever that means, but because of the [confidently assumed] behavior of pressure exponentially increasing with flow, it means that the filter bypass valve would open very soon after a flow of 32-40 qts/m is reached to pass the forced volume of the pump. The pump pumps 58.1 qts at 6000 RPM, so due to it being a positive displacement pump it will pump 32 qts per minute at (32/58.1) * 6000 = 3300 RPM. This means that someplace not far above 3300 RPM the WIX filter bypass valve is going to open. This likely happens at least once every time the car is used except for the most conservative drivers.

This says to me that the WIX 57055 filter is not at all a suitable filter to use on an FB25 engine if you ever press the gas pedal down more than halfway, reving the engine over about 3300 RPM. Or there is that 10 GPM (40 qt/m) number, perhaps it is (40/58.1)*6000 = 4130 RPM. While that is a far less common occurrence, it is still 2/3 of the intended operating range.

Of course what we really need is a pressure vs. US qts per minute flow rate graph through both a clean and a dirty filter, then we could have an idea what is happening. And if we had a pressure vs. US qts per minute curve for the engine, we could figure it out exactly. But we don't.

I would like to use a 15 or 20 micron filter to maximize the life of my engine. WIX and AMSOIL seem to be the likely candidates (Are there others?). I have used AMSOIL for the past 20 years but they were out of stock for many months, and so I looked around, and the WIX do look attractive - and are only a third the cost at Rock Auto! Royal Purple looks very very much like the AMSIOL, but it was out of stock and expensive also.

Can anyone validate my reasoning, or better yet add insight or data to push me one way or another?

My strong tendency is to trust WIX' long long standing reputation as a very highly regarded filter manufacturer, but this analysis, admittedly based on incomplete information from WIX, doesn't support that position. Perhaps a mechanical engineer who understands the fluid dynamics better?

If you got this far, thank you! I hope this is going to be very enlightening, and helpful to many.
 
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I would like to use a 15 or 20 micron filter to maximize the life of my engine. WIX and AMSOIL seem to be the likely candidates (Are there others?). I have used AMSOIL for the past 20 years but they were out of stock for many months, and so I looked around, and the WIX do look attractive - and are only a third the cost at Rock Auto! Royal Purple looks very very much like the AMSIOL, but it was out of stock and expensive also.

First off, thanks for taking the time to write all this up. All good questions and concerns. I just want to address the above paragraph regarding maximizing engine life. I think another way you could do this is to simply change your oil (and air filter) at the "severe service" or "special operating conditions" interval listed in the owners manual. If you did this with the OEM oil filter you may or may not be getting high efficiency 15-20 micron filtration, but in past videos of blue filter tear-downs there does seem to be a lot of consensus that the blue OEM filters have FRAM toughguard media elements. Those are marketed as 99% efficiency at 20 microns. Still this is just speculation since OEM data is not published; however, if you are changing your oil on a manufacturer severe/special OCI then you're not allowing the oil to lose it's properties; thus, it'll hold particles that make it past the filter in suspension and you'll have drained it well before these oil properties break down allowing those particles to cause wear.

All that being said you can't even get the blue 12A or 15A filters from dealers right now due to a supply-chain disruption. The alternate filters a lot of dealerships have been using right now are Champ and ProTec (Wix). I'm not sure a lot of the techs are happy with them, but that's what they decided was okay to use until their OEM supply is restored.
 
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ZeeOSix

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The oil pump internal relief valve pressure less the oil filter bypass valve pressure is what is available to push oil through the engine at minimum. If the oil flows through the filter media easily and the filter bypass valve does not open (Which we hope it does not!) then there is more pressure to push oil through the engine.
This is not correct - the oil filter is just a small "resistor" in the oiling system. The PD oil pump doesn't care is there if there's a bypass valve in the oil filter or not ... it makes no difference to the PD pump.

There will be a max pressure and volume flowing in the gallery before the oil filter when the oil pump is in pressure relief. That volume will go through the filter and into the oiling system. The bypass valve on the filter only operates from the delta-p across the filter. So if that volume going into the filter (along with the viscosity of the oil factor) causes the filter to bypass, that same total volume will still be going through the filter. Only some will be bypassing the media. The PD oil pump's pressure relief valve operates separately and disconnected from the bypass valve in the oil filter.
 
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ZeeOSix

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The WIX filter bypass valve opens at 27 PSI. This would give more margin for tolerances to ensure that the filter bypass valve (Not talked about yet) doesn't open at almost the same time that the first level relief valve opens, the lower apparent pump volume per revolution resulting in the flow that will create enough pressure to open the filter bypass value arriving at a higher RPM.
You will never know, and never be able to "calculate" what's going on unless you actually know the delta-p vs flow curve of the specific oil filter you're looking at. The only way to really know that is a controlled lab test by a lab capable of doing such a test. The graph below is for a Purolator PureOne with hot oil (approx 5W-30 at 200 F). It was done by Purolator in their test lab.

In this case, you can see that at 12 GPM of flow, the delta-p across the oil filter is only 5 PSI. If the bypass valve was set to 15 PSI, then at 12 GPM with the hot oil the bypass would be far from opening.

Keep in mind that filter bypass valves are set for worse case conditions over an expected OCI. That includes cold oil operation, max RPM at times, pressure spikes and also some headroom for media loading with debris, which increases the delta-p across the filter with use.

If you're worried about the a filter bypassing too much on a high pump flowing Subaru, then use filters with the high bypass setting specified for Subarus.

1668920398574.png
 
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Not this again...

I recall having this exact same conversation on BITOG probably 3 years ago about WIX 57055 having a max flow rate of 10 GPM.

Personally I just want to tell everyone to stop caring so much. Just use an OEM filter if you are at all paranoid about anything. If for whatever reason you don't think that is good enough, even though millions of those have been used on millions of Subarus for over a decade and I've never heard one single issue with them being used, all you're going to do is convince yourself that a bunch of stuff really really really super duper matters when in reality it really really really super duper doesn't.
 
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The oil pump has a two-stage bypass, and the first stage is at 21.7psi. Yet the fsm is saying it's 40 psi at 600rpm(idle)..? The first stage is always bypassing?
 
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(2) The bypass valve opened at 23.2 PSI, and the engine back pressure resulting from the oil viscosity must be 23.6 PSI. This would mean that the Subaru filter bypass valve is open over a portion of the 0-6000 RPM range, dropping 23.2 PSI through the valve and leaving 23.6 PSI to push oil through the engine. In other words, every time someone revs the engine over some RPM that is less than the 6000 RPM redline, the bypass valve opens flushing dirty oil through the engine! This is not desirable.
I am not exactly sure if I actually understand your post . Are you referring to the oil filter bypass ? The oil filter bypass valve will allow the oil to bypass the filter when using your numbers when the differential pressure is 23.2 . With the engine running the by pass valve will open when the pressure on the unfiltered side of the element has a 23.2 psi differential of pressure as compared to the filtered side of the element. The oil pump and oil filter bypass do two different things. Push the easy button in this instance and use the oem or a proper rated filter.
 
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ZeeOSix

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It is certainly also true that this is not my field of expertise,
however this is just math, so the conclusion is inescapable UNLESS
there is something wrong with my understanding, or or my analysis (which
are not unlikely) or if WIX was just kidding when they stated that the
maximum flow through the 57055 is 8-10 GPM. I assume that given an
explanation of what they mean by "max flow" would help make sense of
it all.
Yes, the stating of "Max Flow = 8 to10 GPM" by WIX and other filter makers is a big nebulous mystery on what that "spec" is based on.

All you could do is email or call WIX Tech Support and ask them what it means. It would only mean something if they told you what the delta-p is with a certain oil viscosity at the 8 to 10 GPM flow rate, similar to the data points shown in the graph in post #4.

If I had to make a guess on what it means, it could mean the filter is close to hitting the bypass valve setting at that flow rate, but again you don't know what the viscosity of the oil is at that flow rate, which is a big factor in the delta-p produced across an oil filter. Takes a lot less flow of cold thick oil to hit filter bypass than it takes with thin hot oil. That's why engines shouldn't be revved real high until after the oil has got to near operating temperature.
 

Al

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This alarmism on subaru filter bypass settings has been going on for decades. In the 4 subarus I have owned since 2008 I have maybe installed half dozen subaru filters. I have had no problems and have never seen a docunted oil problem attributed to the lower bypass settings on aftermarket filters.
 
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You’re too late, I’ve been running the 5/7055 on two EJs and an FB for several years now and not only have the engines not blown up, the UOAs I have run have been stellar. 😜
Oh that one is fine. The 57712 applies to my engine. It’s got the patented C4 explosive relief valve. Duh!
 

rnsc

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First off, thanks for taking the time to write all this up. All good questions and concerns. I just want to address the above paragraph regarding maximizing engine life. I think another way you could do this is to simply change your oil (and air filter) at the "severe service" or "special operating conditions" interval listed in the owners manual. If you did this with the OEM oil filter you may or may not be getting high efficiency 15-20 micron filtration, but in past videos of blue filter tear-downs there does seem to be a lot of consensus that the blue OEM filters have FRAM toughguard media elements. Those are marketed as 99% efficiency at 20 microns. Still this is just speculation since OEM data is not published; however, if you are changing your oil on a manufacturer severe/special OCI then you're not allowing the oil to lose it's properties; thus, it'll hold particles that make it past the filter in suspension and you'll have drained it well before these oil properties break down allowing those particles to cause wear.

All that being said you can't even get the blue 12A or 15A filters from dealers right now due to a supply-chain disruption. The alternate filters a lot of dealerships have been using right now are Champ and ProTec (Wix). I'm not sure a lot of the techs are happy with them, but that's what they decided was okay to use until their OEM supply is restored.
First, I apologize for apparently dropping off the face of the earth. (1) I ignorantly did not realize that the forum did not send a notification with each reply, and (2) Unexpected holiday goings-on distracted me until last night. Second, thank you for your considered comments. I was (and am) hoping to learn something new!

Regarding "past videos of blue filter tear-downs there does seem to be a lot of consensus that the blue OEM filters have FRAM toughguard media elements. Those are marketed as 99% efficiency at 20 microns.", this is good information if it is true, which sounds like it probably is (Except the part about not being available right now). Regarding oil, I use Amsoil changing between 6 and 7,000 miles, less than half of Amsoil's recommendation for severe service, so I think it is safe to assume that the oil properties have not significantly degraded.

Subaru's indirect recommendation of Champ and ProTec unfortunately falls flat because the WIX website does not list a ProTec filter in their selector for the FD25 engine (2016 Outback with FB25), and the Champ website has only a general flier with warm fuzzy words, and a Red Hat Linux Apache Test Page for their On-Line order facility where I had hoped to do a look-up. I will look again later.

Thanks again, I will keep processing the thread.
 

ZeeOSix

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Regarding "past videos of blue filter tear-downs there does seem to be a lot of consensus that the blue OEM filters have FRAM toughguard media elements. Those are marketed as 99% efficiency at 20 microns.", this is good information if it is true, which sounds like it probably is ...
No way to really know without an ISO 4548-12 efficiency test - just speculation without proof. Subaru may specify Fram to make the media different than the Fram filters.
 
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