99 Wrangler 4.0 Rear Main Seal Leaks at Idle

What do?

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T

the_overlander

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Gents,

I recently acquired a 99 TJ wrangler (RHD) with the inline 6 and five speed transmission. The car is twinlocked, lifted. 32 inch muddies, spotties, rear bar, rock sliders, hardtop etc. etc. etc. with less than 140,000km (or less than 90,000 miles). The car drives great, no fluid leaks and all fluid levels were perfect when I inspected the car (despite it not being driven for almost 2 years). The only issue is that when I idle the car for long periods (e.g. for 45 min, when I was working on it in the driveway), the rear main starts to seep, leading to 1 or 2 drips landing on the ground. If I degrease the engine and go for a 200km drive, the rear main won't even weep. Is this normal? The main seal only leaks at idle. Very concerned!
 
I went to the doctor the other day. I told him that every time I touched the third finger on my left hand to the second toe on my right foot I suffered from an incredible shooting pain in my knee. Any guess as to what he told me? :D
 
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In all seriousness, I voted "other". Don't worry about it. The 4.0 is notorious for leaking, and if it's only leaking one to two drops when idling for 45 minutes (and let's face it how often are you going to idle for that long) and not at any other time is nothing that would concern me.
 
Not a huge thing to worry about. Keep an eye on your oil levels. Get to it, eventually or find a mechanic that won't rape you to do a new seal.


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Just fix the rear main seal. It's maybe a 2-4 hour job depending on the pace you move at. Here's a write-up on how to do it: Rear Main Seal Replacement (4.0)

The 4.0 engines in our Jeeps are notorious for leaking from the rear main seal. In fact, I would say probably 7 out of 10 Jeeps with the 4.0 engine are leaking from the rear main! Fortunately you don't have to drop the transmission to replace it (like you do on most vehicles) so it's really not that bad of a job.

Just fix it and move on, you'll be happy you did, and it shouldn't give you any more trouble for a while.
 
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Chris said:
Just fix the rear main seal. It's maybe a 2-4 hour job depending on the pace you move at. Here's a write-up on how to do it: Rear Main Seal Replacement (4.0)

The 4.0 engines in our Jeeps are notorious for leaking from the rear main seal. In fact, I would say probably 7 out of 10 Jeeps with the 4.0 engine are leaking from the rear main! Fortunately you don't have to drop the transmission to replace it (like you do on most vehicles) so it's really not that bad of a job.

Just fix it and move on, you'll be happy you did, and it shouldn't give you any more trouble for a while.
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Like Chris said"Fix it". Not major but after the fix you won't worry about it. It ain't the end of the world.
That goes for any minor repairs, just spend a little and fix it. Its a "jeep things happen" event.
 
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Germanshepherd said:
I must be a lucky one in that the rms stop leak and a change to 10/40 dino totally stopped my rms leak. Bone dry now for months. Will see how long it lasts.
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Mine actually stopped leaking also, been months and not a drop on the garage floor.
Shortly after i bought my TJ i started using Castrol synthetic.
I believe a member here " think it was Jerry " said that there is additives to help limit leaks in today's synthetics.
 
Maybe I need to use synthetic. Because I fixed RMS and less than a year later, it leaked again. Fixed that one and a little over a year later it developed AGAIN. Hahaa


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Bird said:
Mine actually stopped leaking also, been months and not a drop on the garage floor.
Shortly after i bought my TJ i started using Castrol synthetic.
I believe a member here " think it was Jerry " said that there is additives to help limit leaks in today's synthetics.
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My leak did not start until I switched to synthetic Mobil 1 high mileage. Using penzzoil dino high mileage now. Both oils have conditioners to help with leaks but for me I get the leaks with synthetic.
 
Germanshepherd said:
My leak did not start until I switched to synthetic Mobil 1 high mileage. Using penzzoil dino high mileage now. Both oils have conditioners to help with leaks but for me I get the leaks with synthetic.
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I had the same experience. I switched to synthetic at around 90k miles and the jeep started leaking in multiple places. I switched back to conventional and it no longer leaks except at the pulley.
 
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I had an existing RMS leak when i bought the TJ which was no big deal to me but having the leak completely stop after going to Synthetic oil is a little odd and against the grain of what you hear.
Gotta be somping in there.
 
Brantley, similarly to what you suggest: I was thinking that the grommets on my valve cover are the culprit. There's a ton of oil buildup around them. My valve cover gasket was also recently changed. There's no leaking there. And since my leak is incredibly little, it could just be residual dripping down the back of the valve cover, and down the engine.


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DC0046 said:
It is pretty simple to determine if the leak is coming from the RMS or not.
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How so? Mine dripped off the bottom of
the bellhousing, got my flywheel cover plate all dirty, and being that I was new to Jeeps, I took some pics and sent them to other Jeep owners and they all said RMS too. The new RMS didn't help it even a smidgen. What's your method of checking?
 
If there is no oil dripping down the engine and running onto the bell housing and running to the bottom of it, then what could it be other then a leaking RMS. I can see your point if you have leaks at both your valve cover and the RMS. In that case I would probably use some good degreaser and clean everything well and narrowing it down could be easier.
 
Brantley said:
Might try changing the valve cover gasket first. My "rear main seal leak" was not the rear main seal at all, so the time I wasted and money I paid for parts was for nothing but refreshing my old one I guess. Might be worth looking at at least.
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Brantley said:
How so? Mine dripped off the bottom of the bellhousing, got my flywheel cover plate all dirty, and being that I was new to Jeeps, I took some pics and sent them to other Jeep owners and they all said RMS too. The new RMS didn't help it even a smidgen. What's your method of checking?
Click to expand...

All you need to do is grab a flash light and look at the back of the block, or feel back there with your hands for oil. If you are still unsure, degrease everything thoroughly and then periodically check. If it's the valve cover gasket, the back of the block will have oil on it before it drips down to the bell housing.

Did replace the RMS yourself or did you pay to have it done?
 
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