1999 XJ with 4.0L, 185k miles.

I had my trusted mechanic replace the rear main seal in 2013 but the oil leak started up again earlier this year. He replaced the rear main seal again 2 months ago (this time using a Mopar seal instead of aftermarket) but the leak is back again as of this week.

His theories are that (1) the Mopar seal was bad from the factory, (2) he made a mistake during installation (unlikely, but he acknowledged that this was possible), or (3) a problem with the engine is causing enough vibration for the seal to work its way loose over time. He suggested that I get a second opinion before deciding what to do next.

And before you all tell me that Jeeps leak oil and that's just the way it is... I agree, but I'd like to keep my driveway clean and beautiful if at all possible. Keeping a pan under the Jeep is not an option according to the HOA.

Any advice is appreciated. Thanks!

 

This is what my friend Cruiser54 would say.


Are YOU absolutely positive it's the rear main seal?

Here's why I bring this to your attention.




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.

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.



My Jeep don't leak oil just for your info, don't mean to rub it in..lol Just ppl who say its a jeep thing are lazy to fix the leaks. Not saying you, just the people who say that..are you saying that? lol

 

My cousin replaced his twice. Turns out the back of the valve cover was leaking like crazy.

 

Between my three Cherokees and my wifes Grand Cherokee, we're on 4.0 liter motor #4 and EVERY SINGLE ONE had a leak from the valve cover. I'd look there first before I ripped out another RMS.

 

I degreased the engine and kept a close eye for a few hundred miles. It looks like quite a bit of oil is leaking out of the head gasket. The valve cover gasket is dry as a bone, but when looking at the front of the engine there is a 5-6" area on the left side where a very obvious oil leak is originating from...

 

Very good points to make, before jumping to the conclusion that it's always the RMS. Especially the part about simple physics. Best to do the homework first before shelling out hard earned cash.
Kinda like literally throwing s*** at the wall to see what sticks.
I also agree with the leak thing... I keep my vehicles in good nic and just finished repairing the last little leak in my XJ today. Keep on top of the maint. and then it's much easier to catch when a component starts to go south before it becomes a big problem.

 

The majority of "rear main seal" leaks I have seen turned out to be leaking elsewhere. Usually the oil filter adapter o-ring. The oil comes out and runs along a little ledge on the side of the block and works it's way down to the lowest point where it starts dripping off. The lowest point is where the rear main seal is so it looks like that is what is leaking

 

I had my rear main, transfer case, and rear pinion seals replaced. Still leaking from two places. Back to the shop.

 

The other main place to watch for a leak that appears to be a RMS.. is the valve cover gasket.. right at the back near the firewall since the motor and trans are slightly nose up it will leak straight down from the back. So check there too.

 

I would clean everything real good, pressure washer will help to melt the heavy grease away. Once everything is clean you will have a much more accurate picture of what is leaking, and how much it is leaking.
​​​​​Just go to coin wash with a can of engine degreaser and go to town
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Not a bad idea.... I would just say this.... be very, very careful. Lots of things are more exposed on the Jeep engine bays than on other vehicles. Case and point.... had a good shop recently do a power steering pump swap (didn't want the mess in my garage).
And when pwr steering fluid got on a few things when disconnecting the lines... they accidentally got their cleaner on the ECM... they are not sealed/covered like most vehicles ECM/ECU's are. Well... cleaning fluid got into it and fried the ECM. So they had to replace it. Not a cheap fix.
So just be careful I know you're cleaning the undercarriage...but using high pressure water... s*** can get up to places you may not intend it to.

 

I pressure washed the **** out of my engine bay last weekend. I always use aluminum foil to cover the throttle body sensors and other critical plugs, but I have a plastic cover for my PCM which prevents water from at least dripping on my ecm. No matter what vehicle, you always need to be careful with pressure and electrical connections and sensors. Just don't spray with high pressure or cover them with plastic bags or aluminum foil.

For his purposes, he should focus on the area around the valve cover, the oil filter adapter and the engine block around it, as well as underneath where the engine meets the trans and wherever else the oil is dripping from or on.

Also, make sure you wear eye protection. I used to (and still occasionally) detail cars. The first few times you get a ricochet of pressurized soapy water to the face, you learn quickly to protect your eyes
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