Rear Main Seal? - JeepForum.com
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post #1 of 20 Old 05-03-2021, 01:11 PM Thread Starter
axlaxl
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Rear Main Seal?

So this has been an issue for a while but honestly seems to come and go in intensity. Small oil stains and drips on pavement when I park, from rear of engine. Also, when driving on highway, when I go to an exit and start slowing down I get a light plume of grey smoke out the back, presumably from same oil drip hitting the exhaust.

Fairly small, don't need to refill oil very often and have gone between oil changes without having to add any.

So, does this sound like the RMS? Also, is there any long term danger to not getting it fixed? Just so much money for something so simple that doesn't seem to be affecting anything other than the stain on the street and the occasional annoyed driver behind me driving through a light cloud of oil smoke.

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post #2 of 20 Old 05-03-2021, 06:21 PM
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I have 3 XJs 4.0 one leaks like a sieve has a zillion miles a on it and I check the oil frequently and add as needed..... I would fix it, but not with the miles on it, just not worth it to me, it is better as a misc parts vehicle when it dies at last. It has been leaking for many years.

One is under rebuild and will get the full monty as she goes back together.
Another one is being worked on to replace the high mileage one and just got seals in her this past weekend. The leaks won't kill them, but make working on them a gawd awful mess.
I spent hours with a pressure washer cleaning the one that just got seals in her.
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post #3 of 20 Old 05-04-2021, 06:32 AM
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You probably want to first verify that it isn't the oil filter adapter O-ring leaking. That's a very common point of failure. Cheaper to replace, too. Valve cover gaskets can leak back there as well.

I just replaced the rear main in my 1999. It is a 2-piece seal, so removal of the engine/transmission isn't necessary. It still won't be cheap to pay someone to do it, since the oil pan needs to come off. In order to get that off, the axle needs to be lowered which requires disconnection of various suspension components.

Otherwise, it just pollutes the ground water and storm runoff. I am not one of those huge environmental tree-hugger people, but I also dislike stains on my driveway and I have never intentionally littered ever in my life.
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post #4 of 20 Old 05-04-2021, 06:35 AM
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I will also add that it is likely that your oil leak is a bit intermittent from it building up in the bell housing and depending on how G-forces are acting of the vehicle, it'll either pool up or pour out.
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post #5 of 20 Old 05-04-2021, 07:50 AM
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CRUISER'S MOSTLY RENIX TIPS
REAR MAIN SEAL DIAGNOSIS
OCTOBER 31, 2015 SALAD 3 COMMENTS EDIT


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. A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly.

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post #6 of 20 Old 05-04-2021, 08:52 AM Thread Starter
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Ack.
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post #7 of 20 Old 05-04-2021, 01:29 PM
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What does "Ack" mean?

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post #8 of 20 Old 05-04-2021, 06:04 PM
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Acknowledged
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post #9 of 20 Old 05-04-2021, 07:51 PM
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It does sound like the RMS.

Regardless, long term you will eventually pay the price. Oil will get in rubber mounts, wiring, starter, etc and ruin everything.

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post #10 of 20 Old 05-04-2021, 10:01 PM
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Quote:
Originally Posted by Saudade View Post
Acknowledged
Okay then. To me "ack" is the sound just before my dog pukes.
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post #11 of 20 Old 05-04-2021, 10:02 PM
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Quote:
Originally Posted by rep-tile View Post
It does sound like the RMS.

Regardless, long term you will eventually pay the price. Oil will get in rubber mounts, wiring, starter, etc and ruin everything.
I get the collateral damage from leaking oil, but how can one say it sounds like a RMS when the methodology is to personally inspect?

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post #12 of 20 Old Yesterday, 08:32 AM
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Quote:
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Okay then. To me "ack" is the sound just before my dog pukes.
Yeah, that's falls under the other meaning (used to express mild alarm or dismay), according to Merriam Webster. In computer lingo, it's mean "roger".
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post #13 of 20 Old Yesterday, 03:08 PM
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8 XJ's owned, most had leaky valve cover, several had leaky oil filter adapter, none had real main seal leakage, but it does happen.



Quote:
Originally Posted by axlaxl View Post

Ack.


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post #14 of 20 Old Yesterday, 04:05 PM
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^^^X2.^^^ Both of my XJ's had a leaking valve cover gasket. It sure looked like a RMS. To ensure compliance I used a good schmear of Permatex Ultra Black on the gaskets. So far- no leaks.

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post #15 of 20 Old Yesterday, 10:06 PM
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Yup^^^. same here.

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