Jeep 4.0 rear main seal thoughts

[Tob]

I’m not overly excited to change the seal, just because the upper seal seems to be easily damage despite being very careful.

Rather, I’m thinking of pulling the cap, cleaning the surfaces, replacing the lower RMS and seal with anaerobic sealant.

I’ve not seen many or any threads about taking this approach. The engine only has 4k miles on it.

Maybe it wasn’t fully seal on rebuild. Also, since it leaks and looking at oil levels and engine angle, seems like the lower seal may be the issue.

Would appreciate any thoughts and insight.

Don't worry to much about damaging the upper seal. Fel-Pro includes a plastic tab that helps you to slide the upper seal in without tearing it, but I wouldn't use their RMS. I changed my RMS with Fel-pro a year ago and it instantly leaked worse. A few weeks ago I changed it again with a Mopar RMS and it's been bone dry. If you're going through all the trouble to get in there and change the bottom, change both, and yes, use anaerobic sealer on the mating surface between the cap and block.

Edit after reading the conventional/synthetic conversation: Mine is bone dry with the Mopar RMS and full synthetic oil. I wouldn't rest all your hope on changing the oil to conventional as a bandaid fix to the real problem: the leaky seal. It's possible to have a sealed RMS - be patient and do it correctly and you'll have some hope of having one.

 

[Tob]

Ahh you have the earlier design, i see what you mean now.
I don't know man... im just looking at it from my perspective, if i go through all the procedure of taking it apart, while oil and dirt falls on my face, sweating and feeding mosquitos in this heat, and after all of that it leaks just as much if not worse... that knowledge that i could have changed upper half while i was there

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.... but you know you self better, more power to you

Try applying more anaerobic sealant, i don't think that factory manual calls for enough of it around the seal area.
I think Irun did his once and and his sealant partially did not cure and partially washed away by oil. After i took mine apart for the 4th or 5th time i could see lack of sealant around where seals meet.

Edit: TJ Jim ^ gave you link above to what i did, big thanks to him.

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x2 on applying the anaerobic sealer in this pattern!

 

[eastbloc]

It is a very tight spot, even when putting oil pan back on there is no way to tell if gasket is still on the lip without a bore scope.
in your last 2 pics it looks like your have a dust shield there, that thing will obscure what goes on even more. Here is mine without it

... And it looks like i have oil pan leak

 

[Jms76]

Here is the follow-up on the oil. After switching to the castrol GTX high mileage and running for a while, here is the summary:

Best: pennzoil conventional high mileage, least amount of drips.
Middle: castrol GTX high mileage semi-synthetic. Many more drips than pennzoil.
Worst: Valvoline max-life semi-synthetic. Most leaks, many more than the castrol.

Ultimately my advice is as follows. If you are running a full synthetic and have a RMS leak, you may have luck in stopping it by switching to a semi-synthetic high mileage or conventional high mileage oil.

If you are running a conventional oil and have a leak, switching to a conventional high mileage may help.

If you are running a conventional oil and have a leak, probably pointless to switch to any synthetic or semi-synthetic high mileage oil. Strongly feel it will only get worse.

From my testing and experience with all 3 oils, this is what I found to be the case. Conventional oil best best for reducing, or potentially stopping a rear main leak.

Plan to change my RMS in the fall. Will provide an update afterwards.

 

[HandOverFist]

What really makes a difference on engines using the two piece seals is to offset them so the parting lines are not inline with the caps parting line. Apply just a touch of sealant to the ends of the seals as well as the cap. Don't install them like the factory does.

Exaggerated example here, only need 3/8" or so...(not a Jeep engine image).

 

[Frank M]

It is a very tight spot, even when putting oil pan back on there is no way to tell if gasket is still on the lip without a bore scope.
in your last 2 pics it looks like your have a dust shield there, that thing will obscure what goes on even more. Here is mine without it
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... And it looks like i have oil pan leak

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Check the back of the valve cover to make sure that's not leaking.

 

[Jms76]

I think the offset is a good idea, but my seal does not allow for that. The lower has the little arms on each side that press into the bearing cap. Think the ‘99 engines and prior have this style of RMS.

 

[HandOverFist]

I think the offset is a good idea, but my seal does not allow for that. The lower has the little arms on each side that press into the bearing cap. Think the ‘99 engines and prior have this style of RMS.

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Possibly razor them off and substitute some sealant in their place? I know I would be looking into it.

 

[Cross-Threaded-06TJ]

What really makes a difference on engines using the two piece seals is to offset them so the parting lines are not inline with the caps parting line. Apply just a touch of sealant to the ends of the seals as well as the cap. Don't install them like the factory does.

Exaggerated example here, only need 3/8" or so...(not a Jeep engine image).

View attachment 363681

That offserting works well on sbc.

I like the razor them off and offset and substitute sealant idea for the 4.0. It would be worth a test....

I mean, I don't wanna rush into being the guinea pig on this as mine is dry "for now". If anyone tries this and it works I wanna know though.


Fun fact, my chrysler factory reman 4.0 leaked nicely right out of the box upon start up. Turns out they put the lower seal half in backwards from the reman factory. Must have been a Friday engine......

 

[toximus]

Using a Mopar seal and gasket maker and following the service manual instructions (see post #15) solved my RMS leak after 2 attempts using Felpro and Permatex.

 

[Jms76]

Using a Mopar seal and gasket maker and following the service manual instructions (see post #15) solved my RMS leak after 2 attempts using Felpro and Permatex.

Using a Mopar seal and gasket maker and following the service manual instructions (see post #15) solved my RMS leak after 2 attempts using Felpro and Permatex.

Using a Mopar seal and gasket maker and following the service manual instructions (see post #15) solved my RMS leak after 2 attempts using Felpro and Permatex.

Using a Mopar seal and gasket maker and following the service manual instructions (see post #15) solved my RMS leak after 2 attempts using Felpro and Permatex.

I’ll be interested when I pull the bearing cap on mine. My engine has 6k miles on it and was a full rebuild from ATK. It has leaked since start-up.

I’m thinking two possibilities:

1. There was no sealant applied on the split line / bearing cap. On my engine, they missed thread sealant on threads resulting in water leaks. If there is no presence of sealant, I’ll clean, seal, and put back together without replacing the seal as long as the lower does not have any signs of damage.

2. The engine sat for a while after rebuild, possibly crank and seal may not of had much lube between them when I manually rotated the engine during assembly/install or upon initial startup which may have slightly damaged the seal.

3. I guess the other possibility could be they installed the upper backwards or their aftermarket seals are just not very good.

Hard to say, but I’m really leaning towards no sealant on split line. This is just based on some other misses / workmanship defects on the engine.

Also, think in general it is hard to really see a defective seal. Unless you can see wear, splitting, or some other defect, really hard to tell if it were the bottom, top, or joint that actually leaked.

I just changed front axle seals, it fixed the problem, but old seals had no noticeable defect or wear. Rubber was in good shape, wasn’t torn or signs of uneven wear despite 24 years of use.

 

[Pantera99]

Best: pennzoil conventional high mileage, least amount of drips.
Middle: castrol GTX high mileage semi-synthetic. Many more drips than pennzoil.
Worst: Valvoline max-life semi-synthetic. Most leaks, many more than the castrol.

I started with Valvoline Maxlife, it improved a bit. Last change was Castrol HM & it seems to have gotten a little better.
I saw Napa has a conventional HM oil so I may try that next. Haven't tried the Pennzoil.
I really only get a couple drips per day but yea it's annoying. As long as it's not getting progressively worse I'm not that worried about it.

 

[gajeep]

First time I did my RMS I used a Felpro seal with the ends lined up and a dab of RTV on the ends. It leaked. Second time I used a Mopar seal and 1/4” off-set with nothing on the ends. It did not leak! Also you can confirm the placement of the oil pan gasket with a small round Dental mirror. You will need to examine it before you put the inspection cover back on. You will see if the gasket is where it is suppose to be with this mirror and a flashlight (before you torque it)

 

[macleanflood]

I've done three rounds of seals in six months with Felpros. Have a Mopar in hand...will be my project this week.

-Mac

 

[05 White X]

Your reman engine could have been put together with wear on the crankshaft like mine and leak. I tried three times to seal it. You can see where the seal has worn a groove on the crankshaft. New crank when I made it a stroker no leak.

 

[Jms76]

Started my RMS replacement project today. Couple of observations.

1. Oil pan seal was in place looking good, not source of leak.
2. To my surprise, there was sealant on the bearing cap/split line. Maybe not enough, but it was present.
3. RMS looked good and installed correctly. But as I mentioned, it is hard to tell if a seal is bad unless it is blatantly worn or torn.

4. Lastly, my upper seal had some type of sealant, some white stuff around the outer diameter. It stayed with the block rather that the seal. I’m not sure how to get it out, I’m sure the new seal will maybe force it or peel and push out.

I’ll probably try to dislodge with a doubled up pipe cleaner that I can snake in the groove around the crank. I’ll also try a little compressed air.

I’ve taken pictures along the way. The last pic has the white sealant shown. If anyone has removed or experienced this, would appreciate the insight on how to remove. I don’t think it is a big problem based on the little step on the outside diameter of the seal.

Lastly, after reading all methods for installing. My plan is to use the Mopar RMS, use the guide shoe from my felpro kit. Lube the inner seal with oil. Then apply baby shampoo to the back of the seal as I guide and follow all the way in.

 

[HandOverFist]

Right about now would be the perfect time to try that cutting the ears off/offsetting the seal ends.

 

[05 White X]

I see you have the same groove in the crank as mine, good luck

 

[Jms76]

Wouldn’t say a groove. It is as smooth as the rest of the journal/surface area. No ridge.

 

[Tob]

Mopar RMS, use the guide shoe from my felpro kit. Lube the inner seal with oil.

Exactly what I did. Worked for me. Slow n' steady does it.