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Oil Pressure doubles when hot

wildeagle44
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wildeagle44

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Hi Guys

I'm a bit stumped on this one. Have just put a freshened up motor in the car (rings, standard bearings etc) and ran the motor properly for the first time. Starts and idles perfectly, oil pressure starts at 80psi when cold and slowly goes down to about 38psi after it gets upto temp. As oil temp climbs to 90 degrees the oil pressure quickly goes up about 20psi in 30 seconds and then gradually climbs to 80psi again until i turn it off. After it cools for an hour the process repeats itself.

I have checked and changed oil filter and the turbo drain but couldn't see an issue. Oil is Castrol 15w-40. I have installed a new nissan oil pump and are using the rb30 oil stud with heat exchanger removed. Head and block have been decked, using standard head gasket and bolts. Previously with this engine oil pressures were fine, idled at about 30psi pressure. All the cylinders and plugs were dry, compression came back fine also.

At a bit of a loss as to what to do. I thought maybe the pump pressure relief valve but that wouldn't explain the pressure rising after it get hot? Will drop the oil tomorrow and inspect for anything suspicious. Perhaps be a blockage somewhere?

Any help or tips would be appreciated.

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