Synthetic oil and rear main seal leaks—the myth and the reality!

Keep in mind that the higher the first number before the 'W', the slower it is to circulate when the engine is cold. That's why I run only 5W or 10W engine oils.
 
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Jerry Bransford said:
Keep in mind that the higher the first number before the 'W', the slower it is to circulate when the engine is cold. That's why I run only 5W or 10W engine oils.
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That’s my only concern here in the Inland NW. it can get down to 0*, though it usually only gets down to around 10* on the coldest days. I keep my rig in the garage, so it’s probably 50* in there. I can always try it when Summer comes. Thanks
 
Joeinnewjersey said:
Is Fram conventional oil ok? I’m going to attempt my first oil change in a few days.
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I think pretty much any conventional oil is fine. Good luck on your first oil change!
 
JMT said:
Let’s do it! I really hope this works. Not looking forward to an RMS job!
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Ditto - I have a new filter in my tool box going to pickup some oil this weekend and give it a whirl. Maybe I can remove that oil drip pan under my TJ.
 
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JMT said:
That’s my only concern here in the Inland NW. it can get down to 0*, though it usually only gets down to around 10* on the coldest days. I keep my rig in the garage, so it’s probably 50* in there. I can always try it when Summer comes. Thanks
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FWIW, I run it year round here, and our weather is consistent with yours. If you're worried, you could always try 10W-40.
 
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I'm glad I just stumbled upon this thread because my RMS has been leaking for a while now, its pretty bad too, I'm always leaving drips of oil anywhere I park. I just did my scheduled oil change 2 days ago but this time I'm trying 6qts of Orileys brand SAE 10w-30 High Mileage. They were the only one who had high mileage that wasn't synthetic. I was originally trying 5qt SAE Valvoline 10w30 and a 1Qt of Pennzoil SAE 10w30 High mileage but that wasn't helping. Still only 2 days in, but I'm hoping 6 full quarts of SAE high mileage does the trick. Wish me luck because I really dont want to do a RMS. Ill be reporting back in about a week to see if it helps/stops leaking
 
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I usually buy my oil from Walmart. I get the 10w30. I needed a quart and went to 2 different Walmarts and all I could find was Quaker "Any Mileage" in that weight that wasn't synthetic. All they sell now is synthetic. Now I have to find a new place to buy oil. 😡
 
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KimsJeep said:
I usually buy my oil from Walmart. I get the 10w30. I needed a quart and went to 2 different Walmarts and all I could find was Quaker "Any Mileage" in that weight that wasn't synthetic. All they sell now is synthetic. Now I have to find a new place to buy oil. 😡
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Try O'Reilly's if you have one. As @DylanM345 mentioned, their store brand sells a conventional high mileage 10w30. Nice to see you Kim!
 
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Irun said:
FWIW, I run it year round here, and our weather is consistent with yours. If you're worried, you could always try 10W-40.
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👍🏻 I might just give it a try. Unfortunately I just checked my records and I changed my oil 571 miles ago. LOL
 
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A buddy of mine freaked that mine leaks at the rear main. I laughed. I run high mileage as well, even with 65,000 miles- any 15 plus year old vehicle can benefit from seal conditioners.
 
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Irun said:
Generally, I switch to a 15W-40 on anything over 150k miles. Although I usually use Rotella, this time around, because it was on sale at NAPA, the Valvoline went in.
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Why do you switch to 15W-40? I have a returning RMS leak on my TJ with 235k so I was planning on changing my oil with conventional high mileage soon.
 
pagrey said:
Plenty of people run synthetic trouble free in these things, many on this forum. Obviously this is really aimed at people with leaks.
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THIS!

I'm one of those who have lived on both sides. I always thought Synthetic Oil was just a ploy to get more money. I tried it in my first TJ (a leak-free '03), and I was amazed at how much smoother and quieter it ran. So I stuck with it. No issues, ever.

Fast-forward to my current, not-leak-free, '04TJ. I'm using standard 10w30 and a rear main seep has stopped seeping.

Couple that with the mounds of evidence I've seen in the shop I work in that synthetic oil can leak where a conventional will not... I'm sold.
 
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nathanotis said:
THIS!

I'm one of those who have lived on both sides. I always thought Synthetic Oil was just a ploy to get more money. I tried it in my first TJ (a leak-free '03), and I was amazed at how much smoother and quieter it ran. So I stuck with it. No issues, ever.

Fast-forward to my current, not-leak-free, '04TJ. I'm using standard 10w30 and a rear main seep has stopped seeping.

Couple that with the mounds of evidence I've seen in the shop I work in that synthetic oil can leak where a conventional will not... I'm sold.
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@pagrey nailed it. Interestingly enough, I've always run synthetic in my LJ and it doesn't leak. The TJ was a different story though. It leaked with synthetic, now it doesn't with conventional.
 
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My 2004 with 160000 leaked when I bought it (running synthetic). I changed out RMS, oil pan gasket and valve cover gasket. I run Mobil 1 10w30 full synthetic high mileage and no leaks🤷🏻‍♂️. WHEN it starts leaking I’ll try conventional 😎
 
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