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Unread 06-22-2013, 08:06 PM   #1
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1994 ZJ 
Join Date: Jun 2013
Location: Greenville, SC
Posts: 21
leaks, leaks, leaks!

91 Cherokee 4.0

I have had my XJ for about a month now and am slowly working out all the leaks. I am down to what seems to be either one big or multiple small oil leaks! I just replaced the valve cover gasket and the the plug gasket with a fresh change.

What are the most common sources of oil leaks in post 200k XJs? Where should I start looking before I start pulling things apart?

My oil pressure always just sits at 20. Almost regardless of rpm.

Any help would be awesome!

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Unread 06-22-2013, 08:09 PM   #2
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1995 XJ Cherokee 
Join Date: Sep 2012
Location: Harrisburg, PA
Posts: 759
Valve cover gasket (you already did this), oil-filter adaptor O-rings, and oil pressure sending unit are the most common sources of leaks. Front/Rear-main seal and oil-pan gaskets can leak but the above are more common.
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Unread 06-22-2013, 09:49 PM   #3
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2000 XJ Cherokee 
Join Date: Apr 2007
Location: Syracuse, New York
Posts: 1,904
RMS leaks are pretty common on the 4.0s. Not quite as bad as the AMC manufactured 6 cyls though.
2000 XJ - 3.5'' Lift & Skinny Mudders.
Previous: A CJ, Few TJs and JK.
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Unread 06-23-2013, 08:16 AM   #4
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1990 MJ Comanche 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 10,043
Here's the way for YOU to diagnose YOUR Jeep yourself without any guesswork:

I'd be looking up ABOVE first, and VERIFYING the source of the oil leak YOURSELF.

Everybody, who doesn't own or have to pay for or perform your vehicle repairs, loves to poke their noggin UNDER the Jeep and come out bearing the false bad news that your RMS is leaking.

Many mechanics, friends, people on Jeep forums who can’t see your Jeep from where they’re at, and good old Uncle Bob seem to enjoy telling you it’s the rear main seal. Has a catastrophic ring to it, doesn’t it?

A simple leak at the back of the valve cover or other source could produce the same symptoms. You don’t need to be a mechanic to figure this out. If you have good eyesight and a dim flashlight, you’re good to go on your own. Don't jump on the RMS/oil pan gasket bandwagon right off the bat.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for two simple reasons.

First off, the engine sits nose-up and any oil will run back to the RMS area. Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber's adage apply here. "***** flows downhill".

Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket, in that order, have to be eliminated as possibilities first.

Revised 02-26-2013
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

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Unread 06-23-2013, 08:44 AM   #5
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1994 ZJ 
Join Date: Jun 2013
Location: Greenville, SC
Posts: 21
Well said. At the moment it is very hard to diagnose the source due to layers of burnt on oil and grime.

Is there a "best" way to eliminate the grime to aid my process a little?
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Unread 06-23-2013, 11:32 AM   #6
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1998 XJ Cherokee 
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Location: Canada
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You can mask off electrical connections(cap rotor and fuse box etc) get some good engine degreaser and use it.. Diagnose directly after kts dry and starts to leak, you can go to a "uwash" and get the pressure washer under the vehicle as much as you can to help clean whats there
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