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leak from rear main seal

Hi, I write from italy and my english is not so good. excuse me, may be there are many thread about this problem, but I could not find them. I need istruction to replace a main rear seal on my '90 xj 4.0 limited.
maybe there are a tutorial.....
thanks to all....
 
Check that it is not a leak at the rear of the valve cover
 
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, 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: “Crap 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.
 
I've never had a RMS in a 4.0 be bad enough to worry about fixing it. Other things like oil filter adapter, valve cover gasket, oil pan gasket where it meets the timing cover, and crankshaft seal have been the source of more troubling leaks


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My RMS keeps popping everytime a new one is put in. Even had the motor rebuilt. Few weeks later there it is. Not sure whats causing it but might be better to spend time somewhere else. If you're dead set on fixing it grab a syringe and some dawn dish soap. Soak the upper seal in soap for a bit. Use the syringe to spray some soap into the entry/exit points for the top RMS. Will save you a lot of heartache. Also don't forget to replace the metal U piece and add RTV to the back of the oil pan. Don't try to wiggle the pan out either without dropping your shocks. Not worth the time and effort. Last couple I even took out the lower control arms since my Jeep isn't lifted that much. Anyway good luck! Oh one last thing. Brass punch, socket that fits the non punch side and an ratchet extension makes getting the seal out pretty easy.
 
I've never had a RMS in a 4.0 be bad enough to worry about fixing it. Other things like oil filter adapter, valve cover gasket, oil pan gasket where it meets the timing cover, and crankshaft seal have been the source of more troubling leaks


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On a renix another thing to check is the pcv system. Excess pressure was causing my 89 rms to drip
 
Did my 99 rms a week ago. Had to loosen all but front main cap. Also after ruining the first seal, then the old seal I was using for practice....filed the edge of where the seal gets pushed in. A round chainsaw file worked perfect to just take off the burr. Seal went right in with plenty of dish soap...no damage.
 
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