GT Pony
Well-Known Member
- Joined
- Mar 13, 2015
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- 77
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- Pacific NW
- Vehicle(s)
- 2015 GT Premium, Black w/Saddle, 19s, NAV
When someone says "bypass valve" they have to associate it with either the oil filter or the PD oil pump. I typically use the term "bypass valve" to mean the oil filter bypass valve. I typically use the term "pressure relief valve" when talking about PD oil pumps. The two valves are not performing the same function, and they do not operate in association with each other - they operate independently of each other.I'm not seeing your reasoning on the bypass valve, perhaps I'm misunderstanding your comments. If the valve opens at 100 psi, the system now becomes pressure regulated instead of flow regulated and some flow is diverted by the bleeder valve to cap pressure to 100 psi. I'm not sure what that has to do with the filter pressure drops because once the oil warms up and the system pressure falls below 100 psi, your back to full flow and you can now see the differences in pressure at each measurement point in the system as it relates to the restriction. If you were to keep the oil warmed at the same temperature, say 210F, and just change the filter type, you would see a change in oil pressure on the gauge because the pressure drop across the filter has changed. Flow is the same as long as your NOT in bypass which is only a cold start condition unless your running some crazy thick oil.
In your oiling system diagram, if the oil filter becomes more restrictive, but the PD pump is not in pressure relief (meaning the oil volume leaving the pump is the same), then P1 will increase slightly, but P2 will remain the same (hence an increased delta-p across the filter). The PD pump outlet pressure will just increase enough to force the same volume of oil through the slightly more restrictive "filter+engine" flow circuit. ONLY if the PD pump hits pressure relief is when you would see P2 change as a result of the filter being more flow restrictive. Obviously, if the filter is more restrictive, then the pump will hit pressure relief a bit easier due to the total flow resistance of the oiling circuit. But an oil filter would have to be very restrictive, and/or the oil very cold and thick with high RPM to get the pump to hit pressure relief. As mentioned before, typically the engine oiling circuit is 10 to 15 times more restrictive than the average oil filter.
Racing filters with low flow resistance are useful to racers since they typically use heavier viscosity oil, and they run near redline most of the time. But on everyday cars on the road, if Filter A has 5 PSI of delta-p with hot oil at redline, and Filter B has 8 PSI of delta-p with hot oil at redline, the flow will be the same in both cases because the PD oil pump will typically not hit pressure relief under those conditions. I've tested this out on my C5 Z06 which has a digital oil pressure and oil temperature sensor, and no matter what oil filter I ran, I always got the same exact oil pressure at the same exact oil temperature (with the same oil brand/viscosity) and engine RPM, all the way up to redline because the PD pump could never hit pressure relief even at redline with hot oil. I never tried that with cold oil, because I never went high RPM on that car until the oil was at 200 F.
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