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At idle the relieve valve would never lift even in a properly working motor, as the normal oil pressure, at idle, is less than 10PSI (some trucks simply say 'any' pressure is OK.
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pfarber, what year and engine are you referring to?
This discussion is about a high-pressure 261 (
high-pressure with 261 is redundant, but used here for emphasis).
Look this over and then educate us. I am not a trained mechanic but I have worked on 1940s 216s through 1960s 261a - I might not know what I read in manuals and I am ALWAYS ready to learn (and, I am am often apologizing for my mistakes, by thanking people for educating me).
Ok, what if I told you the OFFICIAL 1954 spec guide for 235/261cu/in engines says that at 1150-1200 engine RPM the oil pump is rated at 4.3GPM (hot oil, 20W) and the OIL PRESSURE AT 1170-1200 engine RPMs is also 45PSI?
AT IDLE, the pump WILL NOT, BY DESIGN pump enough oil (remember, pumps create FLOW, RESTRICTIONS create PRESSURE. Say that second part again) to lift the relief valve? So, at 400-450RPM idle, the pump is, by design, NO WHERE NEAR 45PSI... most ppl seem to agree on 15PSI, but other say less, WHY WOULD A CLOGGED RELIEVE VALVE EVER OPEN? You could weld the relief port shut, and at IDLE, the pump will never spin fast enough to create a system back pressure of 45PSI+ THE FLOW/RPMs are not there to do it.
So, that means, that something AFTER the pump is clogged, as AT IDLE, and UP TO about 1000RPMs the pump WILL NOT generate more than 45PSI to lift the relief valve.
The OP said the pressure "it idled at 50psi but jumped to 160 psi at part throttle" while the relief valve MAY NOT be lifting, its not the reason WHY the system is seeing 80PSI+.
Something is blocking the oil. There are only 4 things in the path of the oil: cam bearings, main bearings, rod bearings and lifters.
One of those, or the galleys themselves, is blocked.
Hows that for explaining my position???
Edit 10:16 - OP said he had to bang out the relief valve with a hammer... but has not reported back if the pressures are normal. I agree that at high RPM the relief valve is a definite culprit... but not at idle, on a summers day with 30wt oil.
