1997 Jeep Grand Cherokee Idle Oil Pressure (4.0 engine)

I am the owner of a 1997 Jeep Grand Cherokee with an inline 6 that I continue to repair as needed.. Currently I have about 144k miles on it and today as I exited the highway and came to a stop the Jeep was idling. I glanced over at the oil pressure gauge and it was almost at zero.. I shifted to neutral and revved the engine and the gauge went back up to 40 psi (normal)..let off and it dropped back down after a few seconds. So every time I came to a stop I shifted in neutral and revved the engine to ~1500 rpm to keep the oil pressure up until I got home..I have changed the oil religously every 3k miles so I was surprised to see this. The rear main seal has a minor leak (for years), and currently no issues with oil level (no major seal fail).

Anyone else on here have oil pressure issues on their inline 6 and was it the oil pump, sensor, or bearings?

First thing to do is purchase a manual oil pressure guage and verify that yours is reading properly. ($10)
Probably a sending unit...but need to verify that.

Get/borrow/rent a mechanical pressure gauge and verify that you have good pressure, but I would suspect the sender. Mine just died at 157K. Hasn't registered more than 45 psi for a few years now, and would occasionally fall off to 0 when it was warmed up. New sender cured that.

I started mine cold and stayed at 40-45 psi idle.. and yes it seems to be intermittent (like yours above)... It was a hot day here in Texas today (95+) and I was driving about 80 for an hour and a half...

The sender is ~$25 at AutoZone, so may just try that first...


I have a love hate relationship with my Jeep.. it does require a lot of TLC... : ).. The Texas heat compounds the issue.

My '90 reads at or near 0 at hot idle and never gets above 25psi on the highway. I dropped the pan to clean the junk out of it 2X and put a high volume oil pump & rear main in it. The oil pressure readings didn't change and I did verify them with a mechanical gauge. The engine has 123K and she's been running like this since I bought her and it doesn't seem to bother anything.
Change the sending unit, put in a new oil pump (4.0 weak point), and drive it.

On the 4.0 engine, which is more likely to fail the pump or the sender?

x3, get a gauge and confirm, might just be a bad sender.

Possible causes of low oil pressure:

Worn cam/rod/main bearings.
Loose rod/main caps--it happens a lot.
Cheap-a** oil filter.
Oil leaks at OFA/oil pressure sender.
Worn oil pump.

Did not bother to do a manual test......Picked up a new sending unit for $27 at Autozone and problem is fixed...


Thanks all for your feedback!

I am having exactly the same symptoms! Just happened, first with a bad oil filter, but has returned. Getting the manual gauge soon to see if it is the sender, or dash gauge.

Does anyone have any thoughts on OP kits? I am looking at the OTC 5610, for about 65 bucks from foxtools.

1990 4.0l XJ