There is a screen, but it's way down in the bottom of the oil pan as part of the pickup assembly. It's pretty course, and usually has a bypass valve that allows oil to get sucked up if the screen gets plugged. A common symptom is you'll have good oil pressure at first, then it suddenly drops down when debris migrates over to the pickup and blocks it.
Low oil pressure is more commonly caused by worn connecting rod and crankshaft bearings, but you'll hear a horrendous knocking noise. There is a pressure relief valve incorporated somewhere in the oil pump housing. If pressure gets too high, that spring-loaded valve opens and dumps some of the oil right back into the pan. It is possible for a small piece of debris to get lodged in there and hold the valve open. That can bleed off normal pressure, and it's more noticeable at lower engine speeds when oil volume being pumped is low.
If there is no knocking noise associated with the low pressure, have the actual pressure tested with a mechanical gauge. If that reads okay, suspect the sending unit. Those cause more low oil pressure readings than actual internal engine problems on a lot of cars.
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Thursday, January 15th, 2015 AT 6:07 PM
