Oil pressure drops off at idle

Okay I'm asking this question for a friend of mine. We put in an aftermarket mechanical oil press. gauge to be sure. The engine drops right to about 0 psi at idle but its not knocking smoking, pinging, etc... it runs fine. The car has new bearings, the crank was polished but not cut. It also has a new oil pump, and new sending unit. Any ideas what might cause it. It does drip at the rear main but I doubt it'd affect the oil press. I'm stumped. Looking for ideas.

first of all every leak no matter how small or big will change oil pressure and for the rest their is probably to much clearence in the bearing that will cause oil pressure loss also .

Well the crank wasn't ground and stock sized bearings were used. The motor doesn't act or sound like it has too large of tolerances. It runs and accelerates good, but at idle the pressure just drops off. I don't think a new oil pump would be bad and he doesn't want to tear it down again until we are pretty sure of what it is. The rear main seal isn't leaking that bad, just a few drips of oil. But its not spraying out or anything like that.

He is now running 20w50 oil.

and new sending unit

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A mechanical guage does not have a sending unit. Oil is fed right into the gauge itself.

Get a true mechanical gauge (even if you do not actually install it in the car) and test again. You should get at least 25-30psi HOT with that oil at idle. That is what I get on my 180K mile stocker.

Well he put in a new sending unit for the dash gauge, and then a day later installed the mechanical gauge. I'll check how he has it hooked up if I see him tomorrow.

im having the same problem... i just re-built my motor and i get no oil pressure on idle but when im off idle i do get pressure... im just wondering if u guys found out what was causing that ?

Scott, if it really does have that low of pressure I would suspect that too much material might have been taken off the crank or perhaps the cam bearings got damaged during re-assembly. As Mike said in the other thread, putting a motor together without checking clearances is just plain asking for it.