[Oldsguy]

Even a healthy engine generates less oil pressure at idle than at 2,000 or 3,000 rpm. What is the numerical value? A fresh/healthy engine will do 40 psi easy, my 455 developes 50 psi at 2,000 rpm and at idle I think it holds 35 psi all day long. An older engine with worn bearing and bushing surfaces might hold 20 psi at idle, any less than that and I would be concerned. If you engine is low then it probably just needs to be rebuilt, then there is always the chance that the gauge is off some too.