Xj1990

Hey when I go down i95 for only about ten miles when I get off my oil will be fine but when the engine goes back to idling on the off ramp the oil psi drops to 0 and bounces a bit. I just did an oil change thinking it was that with 10w-30. Does it need thicker oil? It's a jeep cherokee xj 4.0 1990 114k miles thanks

nickxj94

sounds like the oil sending unit is bad or a wire is loose, check it its right there beside the oil filter.

jakbob

use a thicker oil. or you can just drain about a quart of the oil you have in there now and add a quart of lucas. worked for me.

could be it, but it is more likely wear in the motor.

Xj1990

Ok I'll check the wires, If those are good I'll try the Lucas. Thanks guys.

SHANE 87

I would try running thicker oil

KD3NE

Worn motor at 114,000 miles? If it was abused.

I had a similar problem on my 95.

Pressure was jumping between 0 and 50 even sitting still if I punched the accelerator I could make it jump.

I checked the connector on the sending unit, and it was actually the connector on the sending unit that had failed causing the intermittent reading.

New sending unit and all is well.

jakbob

yeah it could be either or, just giving him more info so if the sending unit is actually good, he doesnt have to repost and wait for more answers.

Firestorm500

A mechanical oil pressure gauge on a temporary hookup would tell the tale for sure.

Xj1990

Added some Lucas to thicken the oil and it keeps it up a bit higher. About 25-30psi. So ill put thicker oil in it when I change it. Thanks

Xj1990

Hey guys long time no see haven't had any probs with the jeep till now, the oil psi shoots up to max and bounces around there. Bad sensor?

KJamesJR

My oil pressure would hang around 38 cold idle. When warm, it dropped down to 5 - 8. The needle would also wobble a bit, not noticable unless you were really watching it. Replaced the sending unit. All is well now. 45 - 50 cold idle, 20 - 25 hot.

Xj1990

Alright sending unit it is. Thanks

tjwalker

The oil pressure sending unit is a VERY common failure on the 4.0 They're inexpensive and easy to replace, but do yourself a favor and spend a few extra bucks and buy it directly from your local Jeep dealer for the best reliability/accuracy/mating with your factory gauge.

Aftermarket oil pressure sending units do not have the best track record.

cruiser54

Gotta ask. What brand of oil filter did you use?

Xj1990

Not to proud of it since I've found recently that they are ****ty. Fram. I'm gonna change it this week when I get paid