Do an engine flush the oil pump pressure relief valve could be sticking or the rod bearings has no clearance creating resistance.
As pressure builds in the oil system, it exerts pressure. A spring-loaded "pressure relief valve" built into the oil pump (or near the pump) opens when pressure exceeds a certain limit (typically 50 to 60 psi) and either reroutes oil back into the pump's inlet or the oil pan. This prevents a dangerous buildup of pressure that could rupture the oil filter or blow out press-fit oil plugs.
At idle, most oil pumps do not produce enough flow to force open the relief valve. Oil pumps that are camshaft driven turn only at half engine speed so output isn't great at idle and low rpm. Even pumps that are crankshaft driven and turn at engine speed (or double engine speed in a few instances) don't pump enough oil to overcome the relief valve spring. The relief valve generally only comes into play at higher rpm when the pump's output pushes more oil into the system than it can handle. Then the relief valve opens to vent oil and limit maximum oil pressure until the engine returns to idle or a lower rpm.
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Saturday, February 14th, 2009 AT 9:23 PM
