Filter Bypass Pressure... Why doesn't this matter?

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Hey BITOGers, I've got a question that ive been wrestling with lately. If an incorrect filter is used with the incorrect bypass pressure, wouldn't that potentially allow unfiltered oil to circulate the engine? If my Toyota specs a filter that has a 20 lb bypass spring but I use a filter with a 10 lb bypass spring, wouldn't that defeat the filtration? Or am I not understanding this correctly? And if so, why is this not a thing we actively worry about?
 
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It does matter, but in testing done here by member Jim Allen years ago, it's not as big a deal as one thinks, except in very low temperatures & high viscosity oils. Some GM & Subaru filters need that 20+ PSI bypass, though!
 
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The bypass is a pressure differential across a plugged filter. A clean(er) filter will have the same engine oil pressure on both sides of the filter. As it plugs up or with very thick oil the bypass will open @ the set pressure. Remember that the engine bearings are what makes the pump build pressure to pump through. Not the filter.
 
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A filter that is not plugged the odds of the bypass opening is low, and most oil will still flow thru the filter. Filtered oil in the sump is already pretty clean, so there are few particles large enough to cause damage to begin with. Then said particle would have to be in the unfiltered fraction of the oil flow and go to a critical area. Avoiding higher RPM even when the engine is cold reduces the chance the filter will bypass. In the old carburetor days, fast idle used to be up to 2K RPM in some cases, and you might have to rev it higher a few times to keep it running. Odds of a filter bypass was higher then. The fuel injection motors seldom exceed 1200 RPM at idle when cold. If you start and drive off in the cold, if you try to keep minimum throttle opening in the first few minutes the bypass should not open. If you are like my neighbor, and start up, back out and then gun it cause he is going to be late to work, again. Yes, you might open the bypass. I would imagine most filters never bypass.
 
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But if I get an aftermarket filter that is specified for my engine, then why worry? If the filter manufacturer is doing more than just matching the threads, they are making sure that the filter does meet the OEM specs for bypass, also, aren't they?
Originally Posted by Gebo
This is one reason I only use OEM filters on my cars and OPE.
Originally Posted by ad244
And if so, why is this not a thing we actively worry about?
 
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Originally Posted by paulri
But if I get an aftermarket filter that is specified for my engine, then why worry? If the filter manufacturer is doing more than just matching the threads, they are making sure that the filter does meet the OEM specs for bypass, also, aren't they?
Originally Posted by Gebo
This is one reason I only use OEM filters on my cars and OPE.
Originally Posted by ad244
And if so, why is this not a thing we actively worry about?
I'd say a good portion of the time we dont know the filters that we use are actually spec'd for our engine. Just that they install correctly. The pressure could be different was my concern.
 
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Subaru specs a high 23 psi for their oil filters. Fram does not make a Subaru specific Ultra filter for the Subaru, but lists the generic Asian fit 6607 or 7317, with a 13 psi by-pass. Why would a large corporation list a lower psi by-pass filter for that application if there was any chance of damage to the engine as a result ? Answer ... there is no chance of engine damage. The lower psi by-pass simply opens slightly earlier, and slightly more frequently, than the higher psi valve. Meaning your oil gets fully filtered 96 % of the time, versus 98% of the time with the higher by-pass. On cold winter days, with cold thick oil, ALL filters by-pass for at least a few minutes. It doesn't seem to hurt anything.
 
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From one website (http://oilfilterdata.com/index.php), i just found that the Fram EG3614 that fits both engines in my sig, is 12 PSI bypass. The Wix equivalent is 8-11. I could not find the Toyota oem filter specs. Thanks for bringing this up--one more thing for us to obsess on cool I would hope that the aftermarket filter companies would give us a filter that is similar to the OEM specs, although as you said we just don't know (unless the specs are published). Does anyone know of Toyota OEM filter bypass pressure? My filter is the 90915-YZZD1.
Originally Posted by ad244
I'd say a good portion of the time we dont know the filters that we use are actually spec'd for our engine. Just that they install correctly. The pressure could be different was my concern.
 
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Originally Posted by ad244
Originally Posted by paulri
But if I get an aftermarket filter that is specified for my engine, then why worry? If the filter manufacturer is doing more than just matching the threads, they are making sure that the filter does meet the OEM specs for bypass, also, aren't they?
Originally Posted by Gebo
This is one reason I only use OEM filters on my cars and OPE.
Originally Posted by ad244
And if so, why is this not a thing we actively worry about?
I'd say a good portion of the time we dont know the filters that we use are actually spec'd for our engine. Just that they install correctly. The pressure could be different was my concern.
I always use a filter that is spec'ed for the vehicle/engine. Never just one that screws on properly.
 
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Originally Posted by FordBroncoVWJeta
The Fram spec'd for my Jetta is 12 PSI. The oem one is 36 PSI. No way would I put a 3x different filter on my car.
Possibly lack of interest for that application. VW can't decide on cartridge or spin-on filters! My application is a 22psi bypass and the Fram XG12060 has so far been in very low production. New GM engines since 2013 have needed this bypass since they take the oil pressure reading from the galleys, not the pump. iirc, Subaru does the same, hence the higher bypass spec.
 
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Originally Posted by paulri
From one website (http://oilfilterdata.com/index.php), i just found that the Fram EG3614 that fits both engines in my sig, is 12 PSI bypass. The Wix equivalent is 8-11. I could not find the Toyota oem filter specs. Thanks for bringing this up--one more thing for us to obsess on cool I would hope that the aftermarket filter companies would give us a filter that is similar to the OEM specs, although as you said we just don't know (unless the specs are published). Does anyone know of Toyota OEM filter bypass pressure? My filter is the 90915-YZZD1.
Originally Posted by ad244
I'd say a good portion of the time we dont know the filters that we use are actually spec'd for our engine. Just that they install correctly. The pressure could be different was my concern.
It's 12-14 I read that a few years ago somewhere from Toyota. The Toyota and Fram for Toyota have very similar bypass valves. You can actually put the Fram valve into a Toyota filter and vice versa. The pressure by hand feels the same. I tried it once. Unrelated but while searching I ran across this video from Toyota. I see a .01 mm filtration claim or 10 microns. Not by the multi pass test they just say it. Actually they say less than 10 microns which has to mean essentially 10. Still it's less. https://m.youtube.com/watch?v=j15x1umneYI
 
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Originally Posted by ad244
Hey BITOGers, And if so, why is this not a thing we actively worry about?
Because there is no way to find out how much oil gets bypassed if any. Very likely some manufacturers specify higher bypass pressure according to some tests from the past when they used 15W-40, 20W-50 oils. The engineers don't like to change specs if the old specs work. I wouldn't worry to much about the bypass pressure if you use a high quality high flow filter. The lower pressure drop across the filter media the lower bypass pressure is sufficient.
 
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Originally Posted by Chris142
A clean(er) filter will have the same engine oil pressure on both sides of the filter.
Not the same pressure on both sides of the filter. However, regardless of the delta-p across the filter, the engine oil pressure will show the same at a pressure sensor located downstream of the filter. Only time that's not true is when the oil pump goes into pressure relief and the oiling system becomes a pressure source of flow instead of a positive displacement source of flow. There is always a delta-p across the filter due to the combination of oil flow, media flow resistance and the viscosity of the oil. Even a brand new filter can have a near bypass delta-p with very cold thick oil and high engine revs, and will have a delta-p of typically around 4~6 PSI with hot oil and lots of flow volume (engine revs) from the oil pump. As the filter clogs up, then the difference between what the delta-p is across the filter and the bypass valve setting becomes less, and therefore the filter can go into bypass much sooner and more frequently than for a brand new filter. The bypass valve setting discussion has happened quite a few times. The bypass valve setting is not only based on the expected oil flow and oil viscosity used in vehicles, but also on the design of the oil filter and media flow performance. That's why you can go to 10 different filter manufacturers and spec the filter for your car and find a difference in the bypass valve settings between those oil filters. You want a bypass valve setting that doesn't kick in too soon and too often, but you also don't want one that's so high that it puts the filter media in danger of failing/tearing because of too much delta-op across the media. Also don't want a bypass valve setting so high that it puts the oil pump in pressure relief before the bypass valve opens, because in that case the engine will be getting less oil volume if the pump goes into pressure relief before the filter goes into bypass.
 
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Originally Posted by ad244
I'd say a good portion of the time we dont know the filters that we use are actually spec'd for our engine. Just that they install correctly. The pressure could be different was my concern.
If you use a filter made by a well known manufacturer, then I'd have to bet that the filter that's specified for you car has been analyzed to have a bypass valve setting that will work on you car. If you don't trust any aftermarket filter manufacturers, then use OEM.
 
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Originally Posted by LotI
New GM engines since 2013 have needed this bypass since they take the oil pressure reading from the galleys, not the pump. iirc, Subaru does the same, hence the higher bypass spec.
I don't know of any engine that has the oil pressure sensor at the oil pump. Most vehicles have the oil pressure sensor located after the oil filter.
 
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Originally Posted by FordBroncoVWJeta
The Fram spec'd for my Jetta is 12 PSI. The oem one is 36 PSI. No way would I put a 3x different filter on my car.
One reason the OEM fllter might be have so high of a bypass valve setting is because the media is much more flow restrictive.
 
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