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Discussion Starter #1
The backstory... bought a 2002 SC with 92000 miles. Zero rust, zero leaks. Having no idea how fresh the oil was (or what oil was in it) I changed the oil as soon as I got it (Quaker 5w30 synthetic) and it’s starting to seep from the rear main or seal holder. Definitely NOT valve covers. So I’m sick over it, and reading all the posts I can find. Found a post about synthetics causing leaks, but was skeptical... UNTIL NOW! Changed to conventional 5w30, and in a few days no more leak. DRY AS A BONE!

Thanks to everyone on this board who has posted their experiences and I hope this helps someone else. I read the procedure on dropping the transmission, exhaust, etc... and this is much easier to try first. I just did the gas tank seal (NOT FUN) and didn’t want to tackle a rear main just yet.
 

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Synthetics in frontiers, or in general? I've been running Amsoi full synthetic oil l for almost 2 decades, in 5 different vehicles, and none ever leaked or had engine issues.
I know that's one of the urban myths about synthetic oil, but it's usually about older high mileage vehicles that just switched over.
 

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Discussion Starter #3
Specifically 1st gen frontiers. Rear main leaks were a common problem. Why it makes a difference... I can’t say. I’ve never had issues with synthetics in any of my other vehicles, and in fact prefer synthetic. I too believed it to be a myth.
 

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Synthetics don't cause leaks. There's various reasons and possibilities why there are leaks. My opinion, previous owner(s) rarely changed oil and used cheap oil. Sludged and clogged up certain seals that would have leaked in the first place. You didn't solve anything. You're just masking the problem. Get that rear seal fixed when you get a chance.

I also run Amsoil Signature Series oil in all my vehicles including my high mileage 2002 Frontier SC that I bought two years ago and it doesn't leak a drop of oil.
 

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YES, The Rear Main Seal Is A Known Issue WIth Our Engines. And YES, Synthetics Don't Cause Leaks BUT Syntheitcs are Thinner Even Though They Have The Same Viscosity So You May Notice Leaks After Switching To Synthetic When You Didn't Notice A Leak Before With Conventional Because It's Thicker.

My rear main seal is leaking too. My valve covers were leaking and i changed them recently at 120k but i'm still leaking (although not near as bad) and i've concluded its the rear main seal. I put in Mobil 1 Synthetic thinking i had fixed the leaking issue and would't have any problems but again, i'm still leaking. My next oil change i had decided that i'd switch back to Dino Oil to hopefully stop the leak. I've seen multiple videos on Synthetic leaking out through seals when there were no leaks before. Even though synthetic is the same weight or viscosity its thinner and can get by seals easier.

I really don't think it matters what type of oil you use as long as its being changed at regular intervals. I've read tons of reviews of people using Walmart Supertech for 200+ thousand miles and having no issues bc they changed it on time. I would agree that synthetic is a superior oil though.

Erick The Car Guy Goes Over the Differences Here and Why You Notice A Leak After Switching To Synthetic. Go To 1:59 - that's where he starts getting into it.

 

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Discussion Starter #6
The video was an excellent explanation, thanks for posting it. Perhaps I should change the title of this thread to “Rear main seal leak... DELAYED!”
 
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