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Help with oil leak

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Oil is slowly leaking from the back of the eninge only when in gear. I've just replaced the timing chain and decided to replace the oil pan gasket from cork to a fel pro one piece and that's when my problems began. I have also replaced the Rms less than six months ago.

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I've found the Felpro one piece still needs sealant on the front and rear parts, which is a good thing when you think about it because the sealant holds the gasket in place while you get the pan up against it.  I use Prestone ultra grey on the bearing cap and front cover, gasket top and bottom AND oil pan.  Just a light coat on each surface prevents oozing yet insures the sealant is sticking to all surfaces. 

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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. "$hit 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
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  • 1 year later...

Best thing I've found for this.  On a weekend (or whenever you don't drive it much is), go to wally world and buy yourself 2-3 cans of their cheapest engine degreaser (about $12 for 3) and a small nylon brush for scrubbing, with a long handle.  Park near water hose (engine can be hot or cold, I like it warm but not just finished driving hot.  Helps break down the grease IMO) and pop the hood.  Disconnect  the battery and hose that block down with degreaser, top to bottom and even underneath.  Tranny too if it needs it.  Wait 10-15 min, and spray off with a hose (no pressure washer, too much chance of forcing water into places it doesn't belong.


Repeat 2-3-4 times or until the engine looks clean, use the brush to break up "gunk" in the crevices that's built way up.  Depending on how clean this gets your engine you can even wipe it down afterwards with degreaser and shoot paint on it if ya like (won't be a professional looking job but it will stop the now bare metal from rusting up on ya if the original paint is missing).


Once the engine is clean, LET IT DRY! Don't hook the battery up for at least a few hours until the motor is dried off.  Then take it for a short drive to warm it up and get the rest of the moisture out.  Park it again and inspect for oil.  Should be easy to find any leaks, use your hands and feel around the back.  Also can park it over cardboard at night to see if you have any drips while it sits.  If none are located, do longer and longer drives until either it does show up or you're convinced it's not there anymore.

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