I have a 2001 Jeep Grand Cherokee V8 Limited W/Off road gearing. When first started up oil pressure is fine. When engine is fully warmed up it is fine. After about two minutes of starting when cold and until it is fully warmed up, pressure drops to zero at idle. gets down to about 20 psi at low rpm, but at 1500 or better its above 40. I was told it is probably the sending unit. I am not sure I agree. Any advice?
Have a direct reading oil pressure gauge plumbed into the sender port. You can either use a T so the sender also reads or you can just leave the sender out of the system and run the gauge direct. Then read the actual pressure when the problem occurs.
You need to determine if you have an engine problem or a gauge problem.
Test it with a remote gage. That’ll be definitive.
Post back with the results.