Oil Pressure Issues

Just would like to say whats up to everyone. i am new here and trying to figure it all out. give me sometime and im sure i will get it. Anyways Brand new rebuilt 302 ho. it only has 3-4 miles on now. I was driving it around the block a few times on its madien voyage. Relized that my oil pressure was low. Took it back to the garage and put a mechanical gauge on it. I was at about 10-15psi at idle. 21 -24 at about 2500rpm. i let it sit overnight and started it the next day. my pressure was 45-52psi. at idle. after it warmed up you could watch the gauge slowly drop off to 10-15psi. then crack the throttle body open and it would only get to about 18-22psi. thats it. Oh yea Brand new oil pump with engine. Any ideas. Thanks in advane

Yes i sure did. But made sure it was solvent cleaned and dried before i put it back on.

Hot tanked the whole works. everything is new when they rebuilt it. I think i may have some junk in the oil pressure relief valve. And it is holding the spring open futher than it should be. Not letting it build any pressure when the oil is hot and thinned out. When the engine is cold and oil thick it has great pressure. but when its warmed up and the oil is thinner pressure sucks. What ya think???????????