Rear Main Seal Leak Cause

Duck Doctor · Jul 27, 2023

Replaced the rear main seal in my 4.0 equipped rig in November. No leaks whatsoever. Rig sat for a few months during the winter without being used. Fired it up last week and oil was gushing from the rear main seal but not until the rig warmed to operating temperature. My guess is about a quart per hour leak, minimum.

Any theories on why this would happen? I could see rear main seal developing a minor leak but not a gushing leak.

WestCoastDan · Jul 28, 2023

I don't have an answer for you, but the RMS leak in our '03 is driving me nuts.
I'm so annoyed with it that I'm thinking engine swap.

macleanflood · Jul 28, 2023

I put four FelPros in until I used a Mopar. Mopar was dry until our last trip...1600 miles to Canada and back down the WABDR in 95 degree weather. Wet now...not terrible...but annoying.

Gushing sounds like something let loose...bearing cap not torqued maybe... think you need to pull it apart and find out.

Did you use red Loctite?

-Mac

Duck Doctor · Jul 28, 2023

macleanflood said:
I put four FelPros in until I used a Mopar. Mopar was dry until our last trip...1600 miles to Canada and back down the WABDR in 95 degree weather. Wet now...not terrible...but annoying.

Gushing sounds like something let loose...bearing cap not torqued maybe... think you need to pull it apart and find out.

Did you use red Loctite?

-Mac

I didn’t use Loctite. This is my YJ and I didn’t notice any reference to using loctite but it makes sense that a bearing cap bolt is loose. Going to drop the pan this weekend

sab · Jul 28, 2023

I did RMS, valve cover gasket, and oil pan gasket a month or two back on my LJ. I don't currently drive it because it's a "work in progress," so, like yours, it sat unfired for a bit. Immediately after doing this work, I noticed a small oil spot on the floor, right below the engine/transmission mating surface. I had to trailer the LJ to the paint shop that was painting some parts for it, and when I started it to load it on the trailer, it leaked quite a bit, leaving a very large oil spot on the trailer bed. I'm hoping that the rear of the oil pan seal is the culprit, as it's tricky keeping the arched portion that goes around the rear crank bearing cap in place. I'm hoping to finally tackle that this weekend. I've been putting it off because I have bad shoulders, and it's quite painful removing the exhaust due to the weight and cumbersomeness.

If I do get to it this weekend, I'll let you know what I find since it sounds like we have the same symptoms. Please do likewise.

sab · Jul 28, 2023

Duck Doctor said:
I didn’t use Loctite. This is my YJ and I didn’t notice any reference to using loctite but it makes sense that a bearing cap bolt is loose. Going to drop the pan this weekend

I think he used red loctite in place of the anaerobic gasket sealant that's noted in the manual. I wouldn't use loctite on the bearing cap bolts.

Duck Doctor · Jul 28, 2023

I should’ve used that anaerobic gasket sealant. Didn’t realize that was the better choice.

macleanflood · Jul 28, 2023

sab said:
I think he used red loctite in place of the anaerobic gasket sealant that's noted in the manual. I wouldn't use loctite on the bearing cap bolts.

Not on the bolts...on the faces of the bearing caps... essentially Loctite is anaerobic sealant.

I think I got my bearing caps up to 500 degrees and it cooked out the Loctite.

Engine coolant temp never went a shade over 212.

-Mac

sab · Jul 28, 2023

macleanflood said:
I think I got my bearing caps up to 500 degrees and it cooked out the Loctite.

If you did, the main bearings are shot. Babbitt melts below 500°F.

Jerry Bransford · Jul 28, 2023

WestCoastDan said:
I don't have an answer for you, but the RMS leak in our '03 is driving me nuts.
I'm so annoyed with it that I'm thinking engine swap.

Before doing anything drastic switch your engine oil to a conventional High Mileage 10W-30 and drive it a week or ten days. Odds are very good the High Mileage seal restorative products will get the seal back in good condition again and stop the leaking. Especially if you're currently using a synthetic engine oil which many seem to dry out the rear main seal. A BMW I used to daily-drive developed a massive RMS leak and when I checked the cost to replace the RMS, which was right at $2k, I switched the oil from its synthetic engine oil to a conventional High Mileage 5W-30 which completely stopped the RMS leak in 7-10 days of driving. The restorative products in High Mileage engine oils don't just plug the leak like a radiator stop leak product does, they can actually restore the seal.

RVAH-13 · Jul 29, 2023

If my memory is correct, I'm now 78, I was told not to use synthetic oils in my tj, only conventional oil. I had a leaking RMS, changed to a diesel 10w-30 and have not had any more leaks. Best luck.

sab · Nov 30, 2024

sab said:
I did RMS, valve cover gasket, and oil pan gasket a month or two back on my LJ. I don't currently drive it because it's a "work in progress," so, like yours, it sat unfired for a bit. Immediately after doing this work, I noticed a small oil spot on the floor, right below the engine/transmission mating surface. I had to trailer the LJ to the paint shop that was painting some parts for it, and when I started it to load it on the trailer, it leaked quite a bit, leaving a very large oil spot on the trailer bed. I'm hoping that the rear of the oil pan seal is the culprit, as it's tricky keeping the arched portion that goes around the rear crank bearing cap in place. I'm hoping to finally tackle that this weekend. I've been putting it off because I have bad shoulders, and it's quite painful removing the exhaust due to the weight and cumbersomeness.

If I do get to it this weekend, I'll let you know what I find since it sounds like we have the same symptoms. Please do likewise.

Update on this - When I finally removed the oil pan again to find the leak (in March of 2024 - it's still a "work in progress"), I found that I had forgotten to put RTV in the corners of the rear arch of the gasket that goes over the main bearing.

5TTTj · Nov 30, 2024

sab said:
Update on this - When I finally removed the oil pan again to find the leak (in March of 2024 - it's still a "work in progress"), I found that I had forgotten to put RTV in the corners of the rear arch of the gasket that goes over the main bearing.

Those late nights will get ya.

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Rear Main Seal Leak Cause

Duck Doctor

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WestCoastDan

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macleanflood

I break sh!t

Duck Doctor

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sab

"Semper Discens"

sab

"Semper Discens"

Duck Doctor

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macleanflood

I break sh!t

sab

"Semper Discens"

Jerry Bransford

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RVAH-13

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sab

"Semper Discens"

5TTTj

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