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Old 07-15-2008, 07:47 PM   #5 (permalink)
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GMC Sonoma - '94 GMC Sonoma
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Originally Posted by ConnClark View Post
...Also most engines have a bypass valve that allows the oil to bypass the filter once the pressure across the filter reaches a certain limit....
My guess would also be that the resistance of the filter element is rather puny compared to the total resistance of oil flow.

But, just the fact that there is a bypass, in case the filter is plugged, or I would also assume in case it's 'just too cold', shows that the filter can offer a real resistance to oil flow.

I notice that my oil pressure is always up around 80 psi when I start, regardless of RPM, and gradually reduces to 40 or so once it is fully warmed up (1/2 hr. driving time). But since it is at 80 psi no matter the RPM I have always assumed it is likely flowing the oil thru the bypass, at least when above idle speed. This is true even when using 0W-30 Mobil-1.

It must take some HP to push that oil but like you say, the filter itself is probably a very small amount of the total oil flow resistance.
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