Rear Main Seal SOLVED - Additional Tips, Tricks, Thoughts and Theories

Jeep05tj

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Location
Geelong, Australia
Hey all, sorry for the overkill but thought I'd write up what I did after I successfully sealed my RMS. I have totalled three attempts over the year and thought I'd talk about the differences and what has and hasn't worked.

Attempt 1: July 2022, Felpro RMS, 3mm offset, RTV on RMS ends, Anaerobic Sealant used, small amount. This attempt held initially for a couple days. I then went on a camping trip, returned home after a week and it was consistently tripping.
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Attempt 2: August 2022, Victor Reinz RMS, no offset, RTV on RMS ends, Anaerobic used, large amount. This attempt leaked once complete but it was a very slow and manageable leak.
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Attempt 3 (Success): July 2023, Mopar RMS, no offset, no RTV on RMS ends, Anaerobic used, moderate amount (very close to workshop guide). There hasn't been a leak and the RMS is holding well. I did a few extra things (documented below) to ensure the it would seal and believe it has all helped.
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This time around (Attempt 3) I did a few different things (not in order) that may help you if you've done it a couple times with no success. I know Chris did a great guide which covers everything really well, but there's a few extra points which could make the difference for you if you just can't get it to seal.

Number 1: Use the Mopar RMS. I've attached a pic of the difference between the lips and IMO, it's substantial. The Mopar RMS kisses the crank easily, whereas the Victor Reinz and Felpro seemingly just touch it. I've used the felpro in the past and it looks identical to the Victor Reinz except in colour. I know people have had success with both of these seals in the past but I doubt they'll last as long as the Mopar, as the lip sticks out at least 30% more. If you order the Mopar seal, you'll need to make your own shoehorn which is pretty easy. Just find some plastic packaging and cut a square out, then cut it to size. The one I made worked perfectly. I also did not put Rtv on the ends of the RMS. The reason I didn't (I did last time) was when I was cleaning the bearing cap, I noticed Rtv had caked on around edge where the seal goes in. It has somehow not set and worked its way in other areas. I also didn't do an offset with the seal, as it's just too risky you'll cut the seal when putting the bearing cap in.

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Number 2: Clean the upper half of the end housing by cutting little squares (1" x 1") of lint free rag, spraying it with brake cleaner and pushing it through with the old seal. Do this 5 to 10 times and you'll see there's a fair bit of muck in there. Some people have suggested spraying brake cleaner in there and then blowing it out with compressed air. Be mindful, if it has grime that's stuck in there, that technique may not get it out. If you do the rag method, the little square should go in easy and shouldn't be forced. If it doesn't want to go in, you've probably cut too big a piece or the material is too thick. Then just use your old seal (cleaned with brake cleaner) and push it through. Between the first and last square (about 10), there was a big reduction in the amount of grime on the last rag. It was only after this step did I spray the entire area with brake cleaner and used compressed air to flush/dry it.

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Number 3: When you start this job, have the back of the Jeep raised so the motor is level or tilting down towards the nose. As your 4.0 tilts down towards the back and when you're doing this job, oil will slowly work its way down into the bearing cap area. My theory is, if the oil is running towards the back of the crank, you might find it'll contaminate the Anaerobic Sealant or rtv around the oil pan before it can set. If the anaerobic seal doesn't set, it'll be washed out by oil. My TJ has a 1" motor mount lift, so this has likely exacerbated the oil running down.

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Number 4: When putting the main bearing cap back on, make sure the threads for the bearing cap bolts are clean (use cotton tips, brake cleaner etc) and the bolts themselves. This will ensure that when you torque the bolts, it will be as accurate as it can be. If there is debris or muck on the threads, it may give over time and you will no longer be torqued to spec. Make sure you thread it up evenly by hand, until the cap starts to mate with the flange. To seat it correctly and as per workshop guide, give a few very gentle taps with with a rubber mallet and a block of wood. You'll see it seat in correctly, meaning you can now torque it. The socket size is 13/16. To ensure it's seating on both side correctly, torque it starting at 20nm, then increasing it 20nm on each side until you get to 108nm.

Number 5: Give the sealants ample time to set before you put oil in and run the motor. The Anaerobic is meant to set within minutes but I don't believe it sets that quickly. The YouTube channel Project Farm tested all the different types of gasket maker/sealer. Anaerobic performed quite poorly and it seems to need perfect conditions to work, with additional dry time (https://youtu.be/ACIzlSanS60). It's no way near as forgiving as rtv. I gave everything 24hrs before I put a drop of oil in.

Number 6: The second time I performed this job, I followed some other YouTube guides with how they applied the Anaerobic Sealant to the main bearing cap. I believe they could be putting too much on, because when I took off my main bearing cap, I found half set anaerobic sealant under the seal. This indicates that if too much is used, it'll just squish into every orifice it can find, and may affect the way the seal seats into the cap. In the below photo, you can see the dried up anaerobic sealant, which had a similar consistency to sand/grit. On the third attempt, I used significantly less anaerobic. I really believe you can use too much sealant where you won't know where it has gone or what it may effect.
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Number 7: To avoid using a metal punch to get the top half of the seal out, go to your local Chinese restaurant and ask for some chop sticks. I've received wooden and plastic in the past. These are so much safer to use and are more forgiving. The wooden chopsticks are great for scraping off baked on anaerobic sealant, which in hard to get to spots.

I know it is very likely the RMS is holding because of the Mopar RMS alone. I think whilst you're in there, you might as well go the extra mile, make sure everything is spotless, take your time and be as thorough as possible. I'm aware people have successfully done the job without any of extra things I did, I'm just putting this out there in the event someone is doing it again and wouldn't mind a few additional pointers.

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I'd also document your bearing numbers and check the tightness of your timing chain. I changed my oil pump too.

Great write up and I too did several FelPros until a Mopar did it... however a recent 1600 mile trip to Canada and back down the WABDR ended up with some slight drippage. Air temps were in the high 90s...water temp was mostly 212 with an occasional needle width over. Injectors got hot enough for heat soak and oil temps got hot enough...IMHO...to cook out some of the anereboic sealant.

-Mac
 
Excellent write up. Thanks so much for the details and pics. I may have another go at it this winter, so I’ll bookmark your writings.
 
Great info! I run Supertech High Mileage synthetic oil from Walmart. I had a slight seeping rear main seal before (maybe a drop on the floor per day). After switching to the High Mileage synthetic oil it's actually completely dry under there.

Side note I forgot to mention...I use 5W30.
 
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Thanks for the feedback guys, appreciate it. I guess the RMS can leak for so many different reasons and the aim should be to eliminate all the chances based on your install.

I forgot to mention that I generally always use 10w-30 mineral oil.

Only once have I completed an oil change where I used a full synthetic oil and I can confirm the RMS leak got worse. Switched back a month later and it slowed significantly.

If it still leaks after switching or using 10w-30 mineral, the RMS is what you'll need to do.
 
I'd also document your bearing numbers and check the tightness of your timing chain. I changed my oil pump too.

Great write up and I too did several FelPros until a Mopar did it... however a recent 1600 mile trip to Canada and back down the WABDR ended up with some slight drippage. Air temps were in the high 90s...water temp was mostly 212 with an occasional needle width over. Injectors got hot enough for heat soak and oil temps got hot enough...IMHO...to cook out some of the anereboic sealant.

-Mac

That's a really good point with the timing chain check and the bearing numbers. I'll add that to the 'to do' list when I'm in there again at some point.

Do you remember how much anaerobic you applied last time? Which of my attempts was it most similar to?

I found this info sheet by Loctite. It's all about their Anaerobic Sealant 518 explaining the amount of time it takes to cure etc. It seems the anaerobic sealant needs at least 24hrs to get to 95%+ strength, with ambient temperatures. Yes, the Anaerobic will start setting within minutes, making a barrier but it'll have very poor low pressure resistance. If people are rushing the curing time, it'll likely never get to 100% strength before it breaks down.

It also talks about Hot Strength which might be relevant to your trip to Canada.

Definitely worth a read.
 

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That's a really good point with the timing chain check and the bearing numbers. I'll add that to the 'to do' list when I'm in there again at some point.

Do you remember how much anaerobic you applied last time? Which of my attempts was it most similar to?

I found this info sheet by Loctite. It's all about their Anaerobic Sealant 518 explaining the amount of time it takes to cure etc. It seems the anaerobic sealant needs at least 24hrs to get to 95%+ strength, with ambient temperatures. Yes, the Anaerobic will start setting within minutes, making a barrier but it'll have very poor low pressure resistance. If people are rushing the curing time, it'll likely never get to 100% strength before it breaks down.

It also talks about Hot Strength which might be relevant to your trip to Canada.

Definitely worth a read.

I think I used Red Loctite 271 and I basically covered the entire mating surface on both sides.

I think my oil temps got way up there... probably not to 500 degrees but enough to affect the seal. Clearly leaking again.

Going to do an oil change... perhaps a fresh batch of high mileage oil will "solve" the issue.

Also planning on exhaust wrap on the pipe from the header to the cat to perhaps keep some of the exhaust temps out of the oil...and maybe help cabin floor temps too. I need a better angle off the header to clear the driveshaft, a flex pipe in the front and a v band clamp forward of the cat to make pulling that section of exhaust easier.

-Mac
 
Wow, some great tips, thanks. I've had a slight leak ever since replacing mine (with Mopar, and following the FSM to a "t", and using conventional HM oil), and just didn't want to go through the hassle of re-doing it hoping that it might be better. Your tips might just give me the motivation to get in there one more time!
 
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Great write-up thanks. I have a slow RMS leak remaining after solving my valve cover leak, so I'm soon gona take on this job soon. Just a quick question on what you mean when you say "offset". Is this when you have both halves of the seal slightly angled so that their connection doesn't line up with the flat part of the metal they slide into? I see that you said you didn't do an offset on the last replacement, but I was just curious.
 
Great write-up thanks. I have a slow RMS leak remaining after solving my valve cover leak, so I'm soon gona take on this job soon. Just a quick question on what you mean when you say "offset". Is this when you have both halves of the seal slightly angled so that their connection doesn't line up with the flat part of the metal they slide into? I see that you said you didn't do an offset on the last replacement, but I was just curious.

Correct and the RMS I used on my 97 had ears and couldn't be clocked.

-Mac
 
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Great write-up thanks. I have a slow RMS leak remaining after solving my valve cover leak, so I'm soon gona take on this job soon. Just a quick question on what you mean when you say "offset". Is this when you have both halves of the seal slightly angled so that their connection doesn't line up with the flat part of the metal they slide into? I see that you said you didn't do an offset on the last replacement, but I was just curious.

Yeah that's right, regarding the offset in the seal.

I didn't do it this time around though because there's a chance you'll cut the seal when installing, and you won't know it until it leaks again. Some people have had success with the offset but it certainly adds more risk so I kept it flush.
 
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Great write-up thanks. I have a slow RMS leak remaining after solving my valve cover leak, so I'm soon gona take on this job soon. Just a quick question on what you mean when you say "offset". Is this when you have both halves of the seal slightly angled so that their connection doesn't line up with the flat part of the metal they slide into? I see that you said you didn't do an offset on the last replacement, but I was just curious.
Before launching into this major job try replacing your engine oil with a High Mileage CONVENTIONAL engine oil like from Pennzoil. High Mileage engine oils have extra restorative products that can help restore the RMS so it's leak-free. It doesn't just plug holes like radiator stop leaks do. Synthetic engine oils are more prone to causing RMS leaks if that's what you're currently running. My previous daily driver car, a BMW, developed a major RMS leak after having lived its life on nothing but a synthetic engine oil (Castrol). After getting several quotes from BMW shops pretty close to $2k I started hitting the BMW forums and every one of them had threads on leaky RMS seals and all recommended switching to a High Mileage conventional. I did that and my RMS leak was cured in 7-8 days of driving.
 
When I bought my Jeep, it had a slow seep from the rear main seal. Left a drop or two on the garage floor every day or two. I changed it to Walmart Super Tech brand High Mileage synthetic 5W30. Seep stopped.

I think the "secret" is the High Mileage not the synthetic vs conventional. But, I'm just some random guy on the internet.
 
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When I bought my Jeep, it had a slow seep from the rear main seal. Left a drop or two on the garage floor every day or two. I changed it to Walmart Super Tech brand High Mileage synthetic 5W30. Seep stopped.

I think the "secret" is the High Mileage not the synthetic vs conventional. But, I'm just some random guy on the internet.

I had a similar situation. However after switching to high millage oil, the leak actually got slightly worse. I added BlueDevil Rear Main Sealer and within two weeks the leak stopped. It has been over 6 months and still no leak.
 
Just an update, still bone dry after a year!

Regarding oil, I'm using 10w-30 Castrol high mileage semi synthetic oil. So far, so good 👍.

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I followed your write up to replace my rms about 6 weeks ago. That’s not as long as a year, but I’ve put a lot of miles on since then and not a single sign of a leak. Bone dry as well.