I recently bought a car with unstable oil pressure. When the engine is cold there is good oil pressure, but when it gets to operating temperature the pressure decreases and the oil pressure gauge keeps going slowly up and down between the high and low on the picture. The tappets also begin to sound a little (only when it's warm). Could it be the oil pump? (I've heard it's easy to replace on the 6cyl engines). And if so, what causes it to vary that much at idle speed?
The car (Opel Monza 3.0 GSE) had been standing in a barn for about a year before I bought it. The cylinder head was fixed in 1997 because it ran to hot, causing the cylinder head gasket to blow. The cooler was replaced at the same time, and a sharper camshaft was installed. I have changed oil and oil filter (Mobil1 10/40, semi synthetic).
Two more questions: Is it easy to determine if the oil pump is worn out? (when removed from the engine). Is it expensive?
Thanks in advance /Agv