Ever since I bought this jeep at idle it always had low oil pressure when warmed up at idle 7-10psi. But after about 3,000 miles it would idle with 7-10psi and then just drop to zero. You rev and it would bounce right back up and then idle down to 7-10 and then just drop to 0. The engine makes no odd noises and the first time it did this it had been idling in the driveway for a few minuets before we noticed it.

I swapped the oil pressure sender but it has the same problems. I did hook up a mechanical guage to it (although its a large sweep gauge 0-300) it is showing 7-10psi approx at all times when idling and never drops to 0. I then did an oil change, removed the "Car-Quest" brand filter for a Mopar Unit and fresh 15W-40 Rotella. Cold start psi has improved from 45psi-55psi but same issue when idling warm.

Any idea why it drop to 0 when i still have pressure? I am going to get a smaller sweep oil gauge to get a more accurate reading also but even though the pressure is low it is there and still what i feel a safe level for a 670rpm idle.

I am not loosing coolant into the oil but I am sending a sample off to have it tested to make sure there are no traces of coolant in there. So main bearings are most likely the culprit of the low oil presssure overall but i still cant figure out why the gauge just drop dead to 0 psi from 7-10 when idling.

2001 Cherokee
128,000 Miles
Auto 4WD

 

sounds like a cracked cylinder head.. check you crankcase cap for white sludge thats a good indiaction of a cracked head.. other than that i would check your oil pump as you already replaced the sending unit..

 

Just changed the oil and it looked fine, have been watching the underside of the filler cap and the dipstick for the typical signs of coolant in the oil and not seeing anything. For the price of a pump it might be worth it, im assuming it fairly easy to drop the pan with the motor in the jeep?

 

low oil pressure seems common on the 00-01 xjs.. I always run 10-40 weight oil and never have oil pressure probs.. pulling the pan wont be hard at all.. let me know how it goes as i would like to change my oil pump somtime soon..

 

As loong as the pan drops easy swapping the pump is a quick job, usually 2-3 bolts and pop the pan back on.

 

I did just take it for a 20min ride and then let it idle for 10min. Never dropped to 0 just sat around 7psi. Tested the RPM as stated 649 in D maybe 700 in park and with the A/C on in D 720ish.

 

you need to check it with oil pressure gauge,

 

i have the opposite problem. I have 40psi at idle and 60psi under any load. Its weird

 

I had the same problem in my 89 4.0. When i would start it i would get around 55psi of oil pressure, and as soon as i got it warmed up, the oil pressure would go down to 5 or 7.... i replaced the oil pump, ran thicker oil, tried everything to give it a fix because i didn't want to have to rebuild it because it ran really good. But finally i decided i would tear the engine out and sure enough my rod and main bearings were shot. The previous owner didn't service it like he should have. But as far as your gauge goes, that's weird.

 

I did

 

It does idle low, 650-670 in Drive after being warmed up, so im sure that doesn't help so i plan to clean the TB soon and see if that helps raise the idle.

 

`600 idle rpms .. that is stated in the haynes manual.. also 13 psi for a warm idle is also stated in the manual..

 

IIRC FSM states warm idle should be 750 in D.

 

that has to be the gauge isnt reading right. mine does it ever so often, its probably a bad connection

 

Yeah ive considered mounting a T off that and hooking up the factory switch and a small 20psi gauge so i can easilly verify oil pressure.