Originally Posted by 69chevyLWB
Fired up my rebuilt 388 chevy (350 bored .060 over and 3.75 crank) and it ran prefect but the oil pressure at 2500 was at 80 psi and would keep climbing the higher the rpms went. Got up to 4000 and she was close to 100lbs! we shut the motor down after this and had no leaks or other problems. Oil pump is in a package from summit which came with a 7 quart pan and a pickup. oil is straight 30w. no oil leaks or gaskets blowing out. just wondering if the relief spring isnt working or whats going on. bearing clearances are around .02-.03
I suppose one big thing to ask is what is the temperature around engine? If it's extremely cold, by that I mean freezing and lower, the oil will be very thick. It could be so thick that even with the bypass open the amount that can pass thorugh the bypass hole is not sufficient to lower pressure inside the engine. If this is in a very cold place I recommend dropping the oil from straight 30 to 5W20. Surprisingly most oils straight, multi, mineral, synthetic all tend to congregate in a fairly tight viscosity range at 200 degrees F, but at freezing and below the viscosity differences are very large. So frozen 30 weight is a lot stiffer than frozen 5W20. But and maybe surprising is that 30 weight and 10W40 follow a pretty similar curve so the heavier multi-weights don't really improve on the very cold viscosity situation over the straight 30.
The other possibility is that the bypass valve is hung up. This could be a spring problem or the valve is physically restricted from opening the bypass hole, this is usually caused by a burr left when the bypass hole was drilled that catches the valve shuttle.