Bepeets

Hi guys,

So I bought a 93 grand cherokee yesterday, and everything seemed fine. Drove around for maybe 3 or 4 hours. At one point I stopped and shut the engine off. Restarted it and then it sounded like it was really struggling so I shut it off. Tried to restart and it wouldnt. Opened the hood and cheked coolant...wasnt empty but it said add. No coolant on me, so I poured some water in. She started back up. I went and grabbed some coolant and filled it up. But now the weird thing is my oil pressure gauge is going crazy. Fluctuating all over the place for a while and now just seems consistently high, maxed out most of the time. Itll do weird things like when Im accellerating itll be about 5/8 of the way to maxed, and when I let off the gas it goes to MAXED. Oh and also I see that most gauges read up to 80 psi but the last number on mine is 5.4? Any advice much appreciated!

dave1123

5.4 is approximately 80 psi or 5.4 atmospheres. You apparently have a Canadian model jeep or something similar. You should install a mechanical gauge to see what you really have. The sending unit might be bad. Jeep says 10 psi at idle is fine as long as it increases above idle. IDK, but 20 psi scares me.

You might want to drain a sample of oil from the pan into a glass bottle to see if you have coolant in it.

rgr4475

First instinct is head gasket. Or bad oil pressure sending unit. Pressure test the cooling system and oil pressure. If there are no external leaks but coolant has disappeared you may have a bad head gasket. Oil will be milky as well.

Nick-B

I second the vote for a failed oil pressure sending unit.

Bepeets

Thanks for the input guys. Im heading on a road trip on Monday and im wondring if you think this is something serious that I should get looked at before I go. Id rather not spend the money right now, but if its gonna die on the way then I obviously would. Please let me know what you think!

dave1123

In my opinion, you need a professional opinion before you commit to a road trip. My crystal ball is kinda cloudy today.

rgr4475

Personally I wouldn't chance a road trip until I have this sorted out.

lgrant

I know this is too late for your road trip but I had similar high oil pressure issues when using a standard Fram filter. Switched to Wix and the pressure stabilized nicely. Pretty cheap to check this possibility.

blueseasons

Ya. I'd second against the road trip idea unless you like to gamble. Its tough enough breaking down at or close to home. I'd never take a new to me used car, especially one that old on a trip until I've driven it for a while and gone over it well enough to be sure its road worthy. One thing I have learned. Everybody selling a car lies.

extrashaky

This is probably too late for OP, but in case anybody else comes across this thread researching this problem:

A pegged oil pressure meter usually* means that the sender or the sender wires are grounding out. The transducer in the oil pressure sender varies the current going to the meter in the dash. If the circuit grounds out, the full current from the battery bypasses the sender, making the meter think there's infinite oil pressure. So it pegs the meter at the high end.

Fixing it depends on where the short is located. Sometimes it's just a matter of replacing the sender. Sometimes the wires in the harness going into the connector will lose their insulation and ground out there, requiring replacement of the connector and a splice into good wire further up the harness. Oil leaking through a bad sender can eat the insulation off those wires, so sometimes you need to do both.

In the OP's case, it sounds like an intermittent ground was causing the meter to fluctuate. Finally the short stabilized and pegged the meter all the time.

*This is usually the problem. However, it's not a bad idea to check the oil pressure with a mechanical gauge before spending money on new parts. If you throw parts at it first and they don't fix the issue, you'll end up checking the oil pressure with a mechanical gauge anyway.

lgrant

The front end of my XJ spent a little time under water on Friday morn. Once pulled out and started, the "oil pressure situation" was normal, along with everything else. Late in the day on drive back to Reno, noticed that the gauge was maxed. I had an extra sending unit on hand (from JY) and tried that yesterday and, to my surprise, it fixed the problem. So far there seems to be a more narrow band (from low to high) but that may be the new 10-W40 - I just changed the oil last Thur.

Conclusion: water can damage your oil pressure sending unit - careful at the car wash.
Cheers,
Larry

jwraymond35

my gauge was maxed out when I bought my jeep. Like 80 I believe. Changed the oil pressure sending unit and that fixed it. It still fluctuates between idle and giving it gas but it never maxes out now.