I agree, if nothing is known about the engine or how it was assembled, we are all assuming there is a problem. If it picks up say 10psi at hot idle with 20w50 is that enough? Is it normal? Who knows. If it was my engine and it had 20w50 in it and only made 15-20psi hot at idle, I’d better see 60-70 at 5000 rpm or my junk would be coming apart for an inspection.