I picked up a used engine that was built about 10 hours ago... Ran it on the dyno and made some big power prior to buying it. At the dyno shop, they had filled it with some Spectro Oil 10w30, but dont remember the exact oil pressure it was running... I do have the build sheet from the engine and on there they used some 15w40 in it initially

That said, I put in some Valvoline VR1 20w50 because thats what I was running with previous motor and has been highly recommended... But now that I got it in the boat and running it seems to be running pretty high oil pressure... Seems to be about 60psi at idle, and gets pinned under throttle which is on a 80psi Faria gauge, alone with a 80psi Faria sender I installed in new motor.
The build sheet indicated a Melling MH77, which is a std pressure/std volume pump... The motor is a gen IV 489 stroker, forged internals, hyd roller cam/lifters if any of that matters... No idea what there clearances are though as the motor was built just last Aug and I just bought it....

Is it possible that they built the motor with tight clearances and using the heavier oil is creating the higher pressures???
Should I back down to the 10w30 or 15w40.... or is it something else I should be looking into?
Comments/Suggestions??
Thanks... Chris

I would first verify pressure with an independent mechanical gauge.

Ok, where would there be another location I can test it at??

You can "T" off right at the sender..Or unhook the elec sender and hook your mech sender. Performance #'s on the Dyno were probably better with the 10-30 but marginally so. for a new build I think 20-50 is too much.

10-40 synthetic might be a better option, however, you didn't say what your water and oil temps were. Cold river water and cool air along with cool engine water and oil temp will leave you pegged.

I know it does't relate to the problem at hand, but this is a great read and valid
http://www.bobistheoilguy.com/motor-oil-101/

I spoke with the engine builder who built this motor and he said to run Shell Rotella 15w40 the diesel oil... So might do that... comments/ suggestion?

Also the avg air Temps are 80-10 and water Temps are 60-80 during the season...

Thanks... Chris

are you running a water t-stat?

Why would anyone run diesel oil in a marine application, to me it doesn't belong in a gas engine, jmo

Yes... 120°

Got me. I've read others ruining the Rotella as well. What would you recommend?