mantycarguy

I recently developed a strange oil pressure problem. New engine with new pump.When cold the pressure will max out at 38 psi no matter the rpms. As the engine reaches full operating temps, the pressures will then climb to 52 psi at 2400 rpms. My thoughts on this leads me to believe that the bypass valve seems to be hanging up in a slightly open position when cold and then frees itself up when warm. I have confirmed this with a mechanical gauge. Because the pump is capable of creating hot pressure of 50+ lbs I dont think this is an Oring problem as the pressures would be low at all temps and lower still with warmer engine oil .Anyone ever seen this?

G Atsma

Never heard of of acting as above, but you never know. What you might do is take the pump out, remove the relief piston, and check for burrs. If anything catches your fingernail, polish it down with VERY fine emory cloth. Also feel the bore for any rough spots and smooth them out as best you can..

mantycarguy

Well ,It was indeed a sticking relief valve. After removing the pump and examining , the valve would hang up cold without fully closing allowing a small amount of the pressure to bypass back into the return side of the pump which was limiting the pressure rise when cold. As the engine warmed up, the piston would then snap shut against the seat in the housing, and the pressure would then rise to normal levels of 55-58 lbs. As this was inconsistent,I can only assume that bore distortion or a burr inside the pump relief housing was the cause. I was skeptical on just cleaning the bore( although I did get the valve to work smoothly) I ended up replacing the pump with a Melling M295. Pressures rise to 65PSI when cold at 1800 rpm and hot idle pressures are at 38 psi. Most of these valve failures seem to stick in the wide open position when warm and the fail to close at all causing a 0 oil pressure reading at the next startup. I guess I was lucky in the sense that I had some oil and not a total failure like most.

G Atsma

Glad you got it resolved! WITHOUT damage!