So, I bought the XJ a couple months ago from a fellow who assured me that the 4.0 had been rebuilt about 10k miles ago. It does run reasonably smoothly though there has been some rather curious 'hacking' done with coolant hoses and vacuum lines. Some of which I have fixed and others will be fixed soon..

The issue I face now is that the rear main seal is leaking, and rather profusely.

Thanks to the two part design, it is not too challenging to fix, but not something I want to do all that often.

What I would like to know is what can cause the RMS to fail quickly, and how to check for such and fix it if necessary...

Thanks for your input.

 

My Jeep is Leaking from the Rear Main Seal per the Mechanic and he says its quite expensive because the Transmission has to be dropped in order to replace it. I saw your post saying that it's not that bad because of the two parts?? I'd really like to know if this is accurate. I don't want to spend the $900 hes asking to replace it.

My Jeep Cherokee is year 2000. Looks Similar to the one on your profile picture.

 

It's a 2 piece seal. I suggest finding a new mechanic yours is trying to bend you over without a reach around.

 

I have a 4.0 L6, which has a two piece rear main seal. To replace it, one needs only to drop the oil pan. No need to drop the tranny. This makes it doable for the average Joe and doesn't even need to lift the truck...just crawl under there and get a bit dirty.

On many other engines, the seal is one piece, which does require a tranny drop and more.


The two piece design is way easier to deal with... Look into what you have and you can save a ton of $

 

If your engine is not venting correctly will make your rms leak. Using a good seal is another way how long it will last.

 

It's a 2 piece seal and mechanics know this. They love the opportunity to do a 2 piece rms if the owner doesn't know any better, since they don't actually have to drop the tranny. If you found a garage that will do it cheaper, and you tell them you know it's a 2 piece and the trans doesn't need to be removed, it might be worth it. It's not exactly a fun job, particularly in crappy working conditions.

There's tons of info here and elsewhere on how to do the job and what to look for before even calling it the RMS (cruiser's tips). It's not all that complicated.

http://www.naxja.org/forum/showthread.php?t=101118

There's a writeup, there's plenty out there with decent pictures, etc.

As Cliff said, ensure that your valve cover is venting correctly (your CCV tubes). Also ensure your VCG and oil filter adaptor o-ring isn't leaking.

Doing this with a one piece seal with a giant transmission like the nv4500 on my C1500 was very, very, very not fun.

 

Rear main seal is a two piece and is easy to fix. Just make sure you don't scratch the crank when taking off the old one. No need to drop the transmission on it.

 

Positive crankcase pressure will just about guarantee a RMS leak

 

This may have been the cause. I drove 100 miles with some vacuum leaks...vacuum leaks relative to the CCV system. I have also had to improvise a fix for the valve cover front elbow that routes to the airbox. In place of that elbow, I used a PCV valve in a grommet.

If the RMS is spitting oil out due to + crankcase pressure, would it stop when the vacuum stuff is fixed...or would it be a loss requiring replacement?

 

It's impossible to say, really - it may have been completely related, may have been completely unrelated.

I know DFlintstone said he was just about to do his RMS but realized his his vacuum lines to his airbox were clogged, and it hasn't leaked since.

I got under mine and looked real good with the drip plate off and am pretty sure my RMS is legitimately weeping a bit, but it comes and goes. Will probably tackle it next summer, for now it's barely leaking.

 

Thanks for the info, Stabs.

I got in there and checked all the vacuum lines; from the airbox and most of the others on the drivers side. I have removed the vacuum hose harness and routed all the hoses directly. All seems well, as best as I can tell. I do need to replace the hose from the front elbow thingy on the front of the valve cover, the hose from there to the airbox. The rear CCV hose goes into a rubber elbow onthe intake manifold, and it needs replacing cus it is stretched out a bit but still holds vacuum.

While I was there, I pulled all the stuff off the throttle body and scrubbed it out just for good measure.

The RMS is still leaking though, so I will replace it today...along with the transfer case rear output seal which has been leaking for a while.

I just hope it fixes the leak permanently cus the oil leaks right on to the exhaust pipe and smokes a ton, and I don't want it to catch fire. That would be totally the suck...

 

Ever read this?




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

 

I have read all of your 26+ tips, including this one about the rear main seal. All of them are awesome and extremely useful. Many thanks.

In this case, it has been the RMS leaking, and I think I found why. Stabs pointed out that pressure in the valve cover can push oil out of the RMS.

While going through all of the vacuum hoses today, I discovered that the rear tube coming from the back of the valve cover was completely blocked up and my impromptu front elbow from the valve cover to the airbox was leaking too.

I fixed both today and now the RMS is leaking far less...though still leaking.

I have a replacement oil pan gasket and a new RMS which I will probably install tomorrow...and also the seal from the output of the transfer case.

 

If you now have that front tube free to vent, wait a bit and see. Some small chance oil is still dripping down out of the bell housing.

 

Excellent idea.