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Hi all. I’m new to the forum. Newly built 350; My oil pressure at cold start is 80 lbs @ 900 RPM idle. Once she warms up (190 T-stat) my oil pressure drops. No knocking, no leaks anywhere visible, no loss of oil volume on dip stick. Straight 50w oil. I’m stumped. New gages installed. I know the oil pump is not the problem because that does not create pressure. Help this 62 year old kid out with ideas. Thanks.
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Straight 50 is pretty heavy. What could be happening is that as the engine heats up and the metal expands, the clearances tighten and the oil can no longer easily pass through them. It is the crank and cam bearing clearances that create oil pressure. I would drain the oil and replace it with SAE30 or 10W-30 and see if the condition improves.
Forgot to mention the motor is high performance. Hence the heavy weight oil. Approximate compression ratio 9.7/1. Live in NC. Pretty hot down here. Also forgot to mention oil pressure is only low at idle when at temperature.
I live in Phoenix where it is much hotter, and I wouldn’t even run 50 here. You could maybe get away with 20W-50, diesels do, but I stand on my recommendation to change the oil to a lower vis. The high performance part doesn’t really factor into this. What is your logic in choosing that heavy an oil? And, just because the pressure is high doesn’t mean oil is flowing. Oil and a filter is a lot cheaper than engine internals, so it wouldn’t hurt to try.
Newly built, huh? As in? Sounds like your crankshaft bearings have improper tolerances for the crank. Those bearings play MAJOR role in overall oil pressure.
Also you got me curious. How is that oil pump has none to do with oil pressure?
Presuming it’s a built engine that was put together from parts…. You did have oil pump housing filled with petroleum jelly before you poured oil in and started her up?Can you temporarily connect a direct-reading oil pressure gauge at the engine to verify your hot idle pressure? Sometimes, dash-mounted gauges lie to you.
Generally speaking, what you describe sounds like excessive clearance at the main bearings, and/or perhaps the rod bearings. And, as has been said, 50 weight oil seems a bit gluey, especially in a fresh rebuild where tolerances would be at their finest during the engine’s life span.
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