Well, I changed out the intrument cluster, and the exact same thing happened. The oil pressure stays around 40 until the engine warms up to over 200, then it goes down to 10psi at idle, and then drops to zero, with a check guages light. I'm so confused. I've changed everything out but the oil pump, so maybe my oil pump is working erratically? Any thoughts, or anyone with a similary issue? Like I said,

I've changed the sending unit, the instrument cluster, and mechanically tested the pump, so what is next?

 

Where did you get your sending unit from? I know auto zone will try and sell you a switch/relay and call it the sending unit (forgot what it is called, but installed on top of the engine instead of by your oil filter). They obviously look identical, but go in two different places on the engine. I replaced my sending unit with a brand new one and still had my gauge pegged. I know you said you replaced it, and it is not the issue, but figured my $0.02 may lead to something.

 

I got mine at a Chrysler service dept(MOPAR matching number). Replaced it, and it wasn't it. Still stumped.???

 

Maybe I should replace the oil pump next? Maybe the guage is reading right and the pump is working intermittenly? Has anyone ever heard of this? I sort of figured that either the pumped worked or it doesn't, and there is no in between? Any knowledgeable experts that can comment on this? thx

 

I had the same thing happen to me in my 2000 cherokee sport. Have you been adding about a gallon of antifreeze every month, more in the warmer months? If so, you may have a cracked cylinder head...common in 2000/2001 xj's.

 

When you hooked the gauge up to it did you leave the gauge on until it heated up?

 

Oil pump relief valve gone bad....or partial stuck open ???

 

FYI....Here is picture of a relief valve in an oil pump...