My 99 Cherokee 4.0L (110K mi) has recently started looking like it might have low oil pressure. When I first fire it, pressure goes to over 40 psi at idle and stays there. Once it warms up (about 30 minutes driving) it holds at about 10 psi at idle, then sometimes will drop suddenly to 0, and the Check Gauges light comes on. It never makes any rattle or other noises that I would expect if there was actually no oil pressure, but it is spooking me. My first thought is a sender going bad, but I am not sure. Any ideas?

Thanks!

 

Search is your friend.



But it's your sending unit.

 

Comes up about once every two days here. You can add "site:cherokeeforum.com" to anything you type into Google and get results only from here. Also we'll forgive that you put this in Cherokee Chat and not OEM Tech

But, since you can type properly and seem nice, here are some key questions and suggestions:

- When was your last oil change? What did you use? Improper weight can cause issues.
- What filter is on there? FRAM, STP, Quaker State, basically anything really CHEAP will cause problems like this including damage to your engine. Mopar, Purolator, WIX, NAPA Gold, Carquest Blue, and anything that's better priced are safe bets.
- Does your oil pressure gauge move when your engine isn't running? It should be zero with the key turned to ON.

- The little passageway inside the engine block that feeds the oil pressure sending unit can clog with sludge that will screw with accuracy. Unscrew the oil pressure sending unit (located just beside the oil filter) and jam a pipe cleaner down the hole. Make sure it's clear.
- The connector can also get plugged with crud or wiring abraded causing a false reading. Remove the connector on the OPSU and spray it out with brake cleaner, make sure it's clean.
- Oil Pressure Sending Unit is notorious for going out and causing this false reading. If all else fails change this.

 

Good information, all! I really love the Jeep, bought it used with that many miles due in large part to the 4L reutation for being pretty bulletproof. Unfortunately, it came with no owners manual, so I am learing my way through this. Any recommendations as to what oil to run? The windshield sticker from the last oil change (about 2Kmiles ago) says 20W-50. I am in Florida, so cold weather is usually not a problem.

Thanks in advance!

 

5W or 10W 30 or 40. Diesel oils are great, like Shell Rotella, Mobil Delvac, and Chevron Delo. Don't skimp on the filter!

That someone put 20W50 in a 2000 with apparent oil pressure issues concerns me...

Is your Jeep loosing coolant?

Get the tests done!

 

No coolant loss... but curious as to why do you ask. (pardon my obvious lack of knowledge... that's why I am here) I just know it runs smooth and strong.

 

2000+ heads crack when overheated, dumping coolant into the oil and resulting in low oil pressure Common "fix" when this happens is to toss 20W50 and Lucas and dump it onto some poor unsuspecting buyer.

 

All I can say at this point is that the oil looks clean, no trace of milkiness that I can see. The temp gauge seems to be right where it should be as well. Thanks for the heads-up, though, I will keep a close eye on it.

 

I am a living testimonial that jeeps can survive low pressure. My very busy DD has had 4psi for the past 3 years. Search my posts.

 

2000...head crack...OP said in post #1 that he has a 1999.



Unless..it's a 1999 Grand Cherokee, then he's dead meat.

 

Duuurrrr... Thanks buddy

 

What happened to the animation in that gif?

It's supposed to look like this.

 

You just won't leave me alone will you? I didn't know there was an animated version. Went through an entire jug of -49 degree windshield washing fluid, half of it hit the glass and I think I inhaled the other half!

 

jpg↑ gif↓

 

OK, so I still have not had a chance to change the sender yet, and still haven't had any funny noises or other troubles. I have still read through some other posts on the subject, and more than one suggests the possibility of replacing the oil pump. First question; is this something that can be done easily? The '99 Cherokee is a 2WD auto.