Would it be a true statement that canister filters with a bypass, will generally go into bypass right after a cold start?
Question about filter bypass.
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OVERKILL
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Not if they have an ADBV as part of the housing to keep it full. And of course oil/ambient temperature, grade and all kinds of other things factor in there too. Differential pressure is what opens the bypass, so if the media flows enough/the oil is thin enough to allow the media to flow enough oil to engulf the engine without creating enough differential pressure to open the bypass, then no.
Originally Posted By: coderighter
Would it be a true statement that canister filters with a bypass, will generally go into bypass right after a cold start?
The great majority if canister/spin on oil filters include an integral bypass. The others like many GM's have the bypass in the engine.
As to the question, depending on how cold the ambient temp (oil thickness) and how fast the engine is rev'd at start up the filter 'could' go into bypass. That said, based on a similar question I asked at the Fram Test Labs, bypass events are relatively rare and very brief in duration.
So based on the contributing factors mentioned, start up would be a time when a filter 'could' go into bypass.
All that said, for many reasons I don't think there has been a study on bypass events, so an exact answer as to frequency and duration is not possible.
I always get a chuckle about bypass. I'm guessing that in 100 hours (or more) of an OCI, the few minutes in bypass are a good thing. If an engine is making chunks specifically during bypass, its terminal. If it isn't, that oil will get a shot at blasting thru the media on the next go around. Many aircraft engines are in constant bypass (no filter). They run 2000+ hours at 70-100% percent power.
Originally Posted By: OVERKILL
Not if they have an ADBV as part of the housing to keep it full. And of course oil/ambient temperature, grade and all kinds of other things factor in there too. Differential pressure is what opens the bypass, so if the media flows enough/the oil is thin enough to allow the media to flow enough oil to engulf the engine without creating enough differential pressure to open the bypass, then no.
I polled several filter boffins on this a couple of years ago and theie reply is that bypass is "infrequent" outside cold starts and high rpm. It's less frequent when you use the correct oil viscosity for the temperature (both engine oil and ambient... basically, to make it simple, the factory viscosity recommendation).
Also, bear in mind that "bypass" does not necessarily mean a full opening of the valve and a total bypass of the media. That's rare outside of a highly restricted filter due to contaminant loading. Many, if not most times in normal operation, oil is still flowing thru the filter media as the overage is bypassing. Many, if not most, bypass events are momentary. Mere seconds or fractions thereof.
Since you can logically predict the most common scenarios for a bypass event, you can take steps to prevent them. 1) Again, run the correct grade of oil (a problem especially If you are running thicker-then-spec'ed oil at low oil temps); 2) cold starts, especially when combined with moderately high revs, and sometimes even "cool" starts (oil not fully warm) with moderate to high revs (agin this is sensitive to oil viscosity); 3) the sudden transition from low to high revs, more so with cool or cold oil (yet again sensitive to oil viscosity). 4) any of the above scenarios are more common with a loaded filter nearing the end of it's service life, but filter loading is highly variable according to OCI and the design of the engine (well-maintained modern engines have few contamination inputs so they are not often load to even 50% of capacity.. again according to the boffins)
While it's generally beneficial to avoid bypass, like anything, this can turn into a fool's quest. The engine doesn't generally suffer greatly from a few seconds of bypass here and there. IMO, where people commonly get into trouble with excessive bypass is when they are running a thicker-than-spec'ed oil without a good technical reason to do so. An example of that is a guy who thinks he's helping his 20 grade-spec'ed engine by running a 40 grade and then short-hopping the engine often (oil is seldom at operating temp) and running it hard to boot. An engine in that scenario might see a lot of bypass events and perhaps enough to take a chunk out of it's service life. On the other hand, if a guy runs his engine at long stretches at high loads and high oil temps, the heavier oil may be justified for the extra protection in that scenario and since the oil is very hot, it's probably running as thin as the spec'ed oil was at more normal loads/temps so bypass is not an issue.
I have a differential pressure setup on my truck and have been monitoring DP for about 8K miles now. I am running 10W30 oil in place of the spec'ed 5W20 (an experiment, OK), and am using a P1 primary filter for which bypass is listed as 7-9 psi... meaning the valve cracks at around 7 psi DP and is fully open at 9 psi. Many filter mfrs list only the fully open or the cracking pressure and often you don't know which (though fully open seems to be more common).
This P1 filter is approaching 15K miles (at which point it will be changed along with the oil) and still, even with heavier oil, the only time I can get it to the cracking pressure is on a cold start if I don't feathter-foot it until the oil temp reaches ~120-150F) or on high revs (5500-ish rpm with oil temp below about 190F). This filter is likely very lightly loaded because, a) I have a 3um bypass, and b) I have a highly efficient air filter (the air filter is the most likely source for engine contamination). Basically, the DP has not changed much since the insto of the DP setup about 8K ago.
So, there you have more than you probably wanted to know about bypass.
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Originally Posted By: Jim Allen
I polled several filter boffins on this a couple of years ago and theie reply is that bypass is "infrequent" outside cold starts and high rpm. It's less frequent when you use the correct oil viscosity for the temperature (both engine oil and ambient... basically, to make it simple, the factory viscosity recommendation).
Also, bear in mind that "bypass" does not necessarily mean a full opening of the valve and a total bypass of the media. That's rare outside of a highly restricted filter due to contaminant loading. Many, if not most times in normal operation, oil is still flowing thru the filter media as the overage is bypassing. Many, if not most, bypass events are momentary. Mere seconds or fractions thereof.
Since you can logically predict the most common scenarios for a bypass event, you can take steps to prevent them. 1) Again, run the correct grade of oil (a problem especially If you are running thicker-then-spec'ed oil at low oil temps); 2) cold starts, especially when combined with moderately high revs, and sometimes even "cool" starts (oil not fully warm) with moderate to high revs (agin this is sensitive to oil viscosity); 3) the sudden transition from low to high revs, more so with cool or cold oil (yet again sensitive to oil viscosity). 4) any of the above scenarios are more common with a loaded filter nearing the end of it's service life, but filter loading is highly variable according to OCI and the design of the engine (well-maintained modern engines have few contamination inputs so they are not often load to even 50% of capacity.. again according to the boffins)
While it's generally beneficial to avoid bypass, like anything, this can turn into a fool's quest. The engine doesn't generally suffer greatly from a few seconds of bypass here and there. IMO, where people commonly get into trouble with excessive bypass is when they are running a thicker-than-spec'ed oil without a good technical reason to do so. An example of that is a guy who thinks he's helping his 20 grade-spec'ed engine by running a 40 grade and then short-hopping the engine often (oil is seldom at operating temp) and running it hard to boot. An engine in that scenario might see a lot of bypass events and perhaps enough to take a chunk out of it's service life. On the other hand, if a guy runs his engine at long stretches at high loads and high oil temps, the heavier oil may be justified for the extra protection in that scenario and since the oil is very hot, it's probably running as thin as the spec'ed oil was at more normal loads/temps so bypass is not an issue.
I have a differential pressure setup on my truck and have been monitoring DP for about 8K miles now. I am running 10W30 oil in place of the spec'ed 5W20 (an experiment, OK), and am using a P1 primary filter for which bypass is listed as 7-9 psi... meaning the valve cracks at around 7 psi DP and is fully open at 9 psi. Many filter mfrs list only the fully open or the cracking pressure and often you don't know which (though fully open seems to be more common).
This P1 filter is approaching 15K miles (at which point it will be changed along with the oil) and still, even with heavier oil, the only time I can get it to the cracking pressure is on a cold start if I don't feathter-foot it until the oil temp reaches ~120-150F) or on high revs (5500-ish rpm with oil temp below about 190F). This filter is likely very lightly loaded because, a) I have a 3um bypass, and b) I have a highly efficient air filter (the air filter is the most likely source for engine contamination). Basically, the DP has not changed much since the insto of the DP setup about 8K ago.
So, there you have more than you probably wanted to know about bypass.
Good question.
A bypass filter takes some of the oil flow and runs it thru a finer filter, in my case a 3 micron absolute filter (micron abbreviated "um:" absolute means it gets EVERYTHING above 3 micron).
Why this changes the equation a bit is that it takes some of the contaminant load that the primary, full-flow filter would have to carry. As a result, the primary filter maintains a lower differential pressure longer because it carries less of a contaminant load.
This is all geared toward longer OCI (Oil Change Intervals) in my case. It isn't clear exactly how much this might ultimately extend the FCI (Filter Change Interval) but I'm changing this filter at 15K (two+ years) regardless, which will be coming up shortly. I wish I could get that filter tested for flow, DP and contaminant loading by a filter mfr. All I have to go by is my DP gauge... which is a substantial amount of useful information... but I would like to see it tested on the same equipment that is used to rate and test oil filters by the mfrs.
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Originally Posted By: OVERKILL
Not if they have an ADBV as part of the housing to keep it full. And of course oil/ambient temperature, grade and all kinds of other things factor in there too. Differential pressure is what opens the bypass, so if the media flows enough/the oil is thin enough to allow the media to flow enough oil to engulf the engine without creating enough differential pressure to open the bypass, then no.
Originally Posted By: Jim Allen
Good question.
A bypass filter takes some of the oil flow and runs it thru a finer filter, in my case a 3 micron absolute filter (micron abbreviated "um:" absolute means it gets EVERYTHING above 3 micron).
Why this changes the equation a bit is that it takes some of the contaminant load that the primary, full-flow filter would have to carry. As a result, the primary filter maintains a lower differential pressure longer because it carries less of a contaminant load.
This is all geared toward longer OCI (Oil Change Intervals) in my case. It isn't clear exactly how much this might ultimately extend the FCI (Filter Change Interval) but I'm changing this filter at 15K (two+ years) regardless, which will be coming up shortly. I wish I could get that filter tested for flow, DP and contaminant loading by a filter mfr. All I have to go by is my DP gauge... which is a substantial amount of useful information... but I would like to see it tested on the same equipment that is used to rate and test oil filters by the mfrs.
Originally Posted By: Tegger
Don't ALL modern automotive canister filters have a bypass?v
Originally Posted By: coderighter
Hmm... Ok, here's another silly question. Wouldn't filtering down to 3 micron be removing some of the additive package in the oil?
So in the differential pressure calculation, if the measurement between the pump and filter was say, 5 psi and the outlet of the filter was free flowing, the static pressure in the filter caused by the media would be 5 psi correct? If so, then if the outlet was loaded to 40 psi, the gauge between the pump and filter should measure 50 psi, correct?
Originally Posted By: coderighter
So in the differential pressure calculation, if the measurement between the pump and filter was say, 5 psi and the outlet of the filter was free flowing, the static pressure in the filter caused by the media would be 5 psi correct?
Originally Posted By: coderighter
If so, then if the outlet was loaded to 40 psi, the gauge between the pump and filter should measure 50 psi, correct?
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