oil pressure problem

I have a 6 cyl AMC in a 76 DJ5 Postal Jeep. Cold it has 50 lbs oil pressure, but as it warms up it drops all the way to zero at idle. It will rise to about 20 lbs if you rev it up after its warm, but drops to nothing as soon as you put it in drive. The engine sound good, and the last owner said it was always this way, but I've never had an engine lose so much pressure from cold to warm,and I would like to correct that if possible. What do you think? Is this common with this engine? Thanks for the advice.

 

Not common in this engine. However, problems with the OEM oil pressure gauges are. I'd suggest that you get an inexpensive mechanical oil pressure gauge and verify the reading. With no bad noises (esp. no lifter noise !?), it seems very unlikely that your oil pressure could be that low.

If it really is that low, I'd first look at the oil pump for wear or a broken pressure relief spring, and then measure the bearing clearance with plastigage. If the bearing clearance is excessive, not much you can do except rebuild or replace the engine.

 

As Comparrison:
Fresh rebuilt 258 with 1000 miles on it:
Cold Idle 50~65 PSI (I can not remember the exact number)
Warm Idle ~20 PSI
These readings are from a Autometer Guage with remote electic sender.

Definately verify the oil pressure. If it is good then no worries. If it is low then the most probable cause unfortunately is worn bearings which will require a rebuild. But like Tim said. It is not expensive to drop the pan and replace the pump. So that would be a good starting point.

 

The good news is that these engines are very durable, and inexpensive used (or even free if you look around), so don't worry too much.

 

Thanks, Guys for the advice. I had an oil pump go bad in a 81 cj5 with the Iron Duke 4cyl. Idling around would cause some loud noises in the valve train after a few minutes. I think I'll try letting this one idle without any reving and see if any noise developes. If nothing happens I'll buy another gauge, if it gets noisy, I'll change the pump. Do they make a Hi-Performance pump for this engine? If a new pump doesn't help, maybe I'll try a motor honey. Thanks again