Oil pressure went crazy and now it looks like I'm leaking oil

[StraightToPlaid]

My XJ has about 1000 miles on it since I bought it, 100k on it total. At some point it looks like it leaked a bit from the oil pump/filter/sending unit area but looked like it had been fixed.

I was driving it to work yesterday and while it was still cold I was idling at a light. Since the engine was still cold I would expect the oil pressure to be around 30-40 psi. Well, all of the sudden the pressure started bouncing about 20 psi. Now it looks like I've sprung an oil leak. Before I pull things apart what should I be looking for?

Details on the jeep:
'97 Cherokee Country
100k
4.0L engine

 

[birchlakeXJ]

You need to spend some time isolating the leak. Leaks can be notiously difficult to determine cause as oftentimes where it is dripping is a ways away from the source of the leak; fluids MIGRATE. Get the best light you can find and get it up on a hoist if you have access to one. Areas to specifically look at would be valve cover (especially at the back), oil filter adaptor (and sending unit), oil pain, rear main. The oil pressure fluctuation could easily be something as the sending unit; a very common hardware fail on the 4.0. Good Luck!

 

[Shorty]

rarely will the RMS, VC gasket , or filter adapter cause a drastic drop in pressure. I'd hazard a guess that you've got a leaking/ bad sending unit. As stated previously, they're problematic on all of these motors and a new one should solve both problems at once. It never hurts to verify first that it's leaking, but I'd bet dollars-to-doughnuts that it's reading low either way....

 

[ChiXJeff]

Another vote for the oil pressure sensor. Make sure you get a replacement for a gauge package, the sender for the idiot lights will read 0 or off the scale.

I assume you've got the full gauge instrument panel, you refer to psi.

 

[StraightToPlaid]

Another vote for the oil pressure sensor. Make sure you get a replacement for a gauge package, the sender for the idiot lights will read 0 or off the scale.

I assume you've got the full gauge instrument panel, you refer to psi.

I'm pretty sure it's the oil pressure sending unit or something similar. When I got the jeep it looked like that had been replaced and there was an oil slick down that side of the engine starting at the oil pump/filter/sending unit area.

Will I be better off just grabbing a MOPAR replacement? It will be a couple bucks more but I'd like to avoid this headache in the future.

 

[ChiXJeff]

I've had an Autozone replacement on my Heep (after an IP replacement) for several years.

 

[Shorty]

price the Mopar unit and see if it's really much more. I don't think it's that much more than the aftermarket ones-- that being said, the fact that they're known to be a problem in the first place doesn't fill me with much confidence in the factory original to begin with.

 

[lawsoncl]

If you go to the dealer, get the set of 3 o-rings that go in the filter adapter housing. Should only be a few bucks. They are a common leak area and fairly easy to replace. Agree on a possibly damaged pressure sender as they are easy to whack with the oil filter and they do wear our (think of a scratchy volume knob).

You did check the oil level right? My MJ starts getting low idle oil pressure if it gets really low on oil. Also avoid Fram filters as they tend to plug up rapidly and drop your oil pressure as well.

 

[RichP]

Replace the sender, I got one from AA for I think $24 or so. Took me 4 minutes, just make sure you have the correct depth deep socket, in my case I bought one at Sears that was a 6 point, the 12 point would not grab the sender. And it's a really deep socket too, it holds the sender and still allows the ratchet extension to seat into it.

 

[4x4life05]

awesome thread, but I have another question, what if it isn't the sensor but the actual plug you put into the sensor?

 

[RichP]

awesome thread, but I have another question, what if it isn't the sensor but the actual plug you put into the sensor?

The plug is just a plug, I had an intermittent one on my 97TJ, sometimes it worked, sometimes it didn't. I replaced the sender, fixed. The problem was the connector in the sender itself, if I tweaked the wires just right it would work till the next bump. The biggest hassle was getting a good deep socket to put the new sender in with and get the old one out, the ones I had were not deep enough. Finally found one at Sears that worked great for $12.xx.

 

[Shorty]

awesome thread, but I have another question, what if it isn't the sensor but the actual plug you put into the sensor?

if the plug was the issue, he wouldn't have sprung a leak also...

 

[4x4life05]

found out what it was...it was a bad sensor, there shouldn't be any oil getting behind the sensor where the relay unit is. thanks anyways guys