I have a 2001 XJ and on cold starts my oil pressure gauge reads roughly 40 psi (normal). As the engine warms up the pressure starts decreasing to the point when I come to a complete stop the pressure drops to zero and the check gauges light comes on. It does not run rough. I was about to replace the sending unit this weekend, but I wanted to know if anyone has any other ideas what it might be.

My first guess is sending unit..Now keep in mine it is normal to start high and as the engine warms the oil warms and you will drop oil pressure at idle but should never get below about 10-13...So replace the sending unit then see if that fixes it..If not then go rent a compression checker and check cylinder compression if all checks then possible an oil pump or clogged up pickup tube..

Forgot to say that this all happened after I got my oil changed. There are no leaks and it was not underfilled. I wanted to replace the sending unit at $18-19 before I started messing with anything else.

Haoppened right after an oil change..hmm Who did the oil change?Could be the oil filter wasn't put back on properly even if it's not leaking..

Allen Samuels Dodge. I used to be the sales manager there and have been going there for oil changes ($12.40 drive out) ever since. Mopar oil filter and it looks like it is on straight, but I haven't gotten up under the truck to check it. Hook'em Horns!!!!!!!

was it overfilled? if your gauge says you have no oil pressure and your check engine light comes on i wouldn't drive it til you find the problem

Check engine light has not come on and the pressure reads between 15 and 30 psi while driving depending on RPMs. No rough idle and no tapping noise from the engine

It is easy to damage the sender as it sets so close to the filter. Many ham fisted service guys damage hem or even breakthem completely off.
It was one of the few design flaws with the 4.0L engine IMHO.
Replace it and make double sure the wire is making a good connection, then see what your pressure reads. If it is still low replace the sender with a mechanical gauge and see what that reads at operating temp. That will be the best way to tell if you have a real problem or if it is a pseudo-problem.

Is there a possibility that they could've put a lighter weight oil in?? That could cause a drop in oil pressure. I'd replace the sending unit, mine went out, and they are cheap and easy to replace. HTH!!

Right on brother...Can't wait to seem the Sooners win another...Oh and head to the Big 12 to show Mizz who's boss...

Someone needs to come put this damn gasket on my distributor..I hate leaking oil out that damn thing..

Base gasket where it bolts down to the block or internal o-ring OKC which is in need of replacement?

Thanks for your help!!!!!

Hook'em!!!!!!!

You two have a problem with my Horns????