Just installed motor fresh from engine builder. It is a 1995 vintage Marine Power 502 415hp. Running merc multigrade oil. Initial start up it had 40psi. I thought this was a little low but attributed it to the multi grade oil (have always used straight 40).
Took her out, oil pressure dropped as engine warmed up. Got as low as 30psi while at cruise rpm of 3600. I installed a mechanical gauge. It read within 2 lbs of in dash unit. Are there any possible issues that are external of engine that can cause this? I want to eliminate all possible causes before I call the builder.

Thanks,

Steve

You could try cutting the filter open to look for metal. If that is clean go up in oil weight or even try a rotella deisel oil. Chances are though something is amiss internally.

Dented oil pan? That's external?

Main bearings are the usual culprit. Sorry.