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Mercruiser 50 High Oil Pressure

anssec66

New member
I have a 1998 Mercruiser 5.0 s

I have a 1998 Mercruiser 5.0 sterndrive that is carbureted. It has 260 hrs on it. The oil has always been properly maintained. The oil pressure on idle is approximately 45 psi and when I am cruising at 4000 rpm the psi jumps to 70-75. I am running Mobile 1 10w30 full synthetic. The oil is brand new. Any ideas.
 
"Brad:
Oil Pressure @2000 RP


"Brad:
Oil Pressure @2000 RPM should be between 30-45 PSI. You are on the high end @ w/45 PSI @ idle assuming your idle RPM is about 650-750 RPM. Check for corrosion at the sender and at the gauge--clean the terminals and the post on the sender with light sandpaper. Increased resistance from corrosion would increase the pressure reading.

If the wire terminals are clean and the pressure is still the same, install a good manual oil pressure gauge in place of the sending unit to get an accurate pressure reading. If the pressure drops, the OP sender is most likely out of range and should be replaced. Could also be a defective gauge or internally corroded wire.

If the pressure increase occurred right after an oil and filter change, change the filter and see what happens. Could be the wrong filter or just a bad filter. Is the oil weight you are using due to the cold weather? Guy"
 
"Increased resistance will low

"Increased resistance will lower the reading, not raise it. The standard test for an oil sender is to short the wire to ground and it should peg the needle, not drop it to zero.

Making sure the terminal is clean is a good idea but I would suspect the sender. If the wire is removed and the needle drops to zero, the gauge should be OK.

How long has synthetic been used in this motor? Usually, the pressure will drop a bit when this is used instead of regular oil. Check the resistance of the sender with the wire removed and compare that with a new one."
 
Jim:
You're 100% right.


Jim:
You're 100% right. Thanks for catching my bass akwards statement. Sorry about that Brad.
Guy
 
Guy and Jim Thanks for your su

Guy and Jim Thanks for your suggestions. I did make a mistake in my original message and the oil currently in the motor was mobil 1 15w50 full synthetic. Today I bought an oil pressure gauge and found the engine oil pressure was still running high. I changed the oil with full synthetic 5w-40 and that seems to pull the oil pressure down to 38psi during idle and 50 at 2000 rpm. This was only done with huffers on parked in the driveway for a short period of time. Next time I take it out will be the true test. Thanks for everything.
 
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