Could synthetic oil be causing my oil leak?


Bryan

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I just completed installing an ATK remanufactured engine in my 95 YJ 4.0. I just change my break-in oil after 250 miles. I've been pretty excited that I didn't have any oil leaks. I changed the oil with 5W30 synthetic oil (still cold here in Utah). To my disappointment I have a small oil leak. It looks like its coming from my rear seal (oil pan looks OK) My question is.... could the viscosity of synthetic oil actually be causing my oil leak?
 
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Bryan

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Nope. The viscosity of 5W30 synthetic oil is the same as the viscosity of 5W30 non-synthetic oil.

Thanks for your response... you are correct. I had to find out for myself and got all anal and changed the engine oil back to regular 10W-30 and..... it still leaks! Through the rear seal- I assume. so thanks for confirming that.
 

jeepjoe43

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I haven't had 4 or 6 apart, but I've been through a number of AMC V8s, all with split rear main seals.
Looking at my Chilton, the 4s have 1 piece seal, but the 4.0 has the same crappy 2 piece seal.
And in my experience, they ALWAYS leak some.
 

SirDoopYJ

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I plan on working on my RMS (4.0, 2 piece) this weekend. I can let you know how it goes when I am done if you are wanting to fix yours to fix the leak. If it is just a drip, honestly, I would not worry about it. The only reason I am doing mine is because I am burning more oil than I should be. From what I saw on videos it does not look hard, but you will be on your back the whole time and you have to be careful not to touch/scratch the bearing when removing upper seal.
 
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jeepjoe43

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I plan on working on my RMS (4.0, 2 piece) this weekend. I can let you know how it goes when I am done if you are wanting to fix yours to fix the leak. If it is just a drip, honestly, I would not worry about it. The only reason I am doing mine is because I am burning more oil than I should be. From what I saw on videos it does not look hard, but you will be on your back the whole time and you have to be careful not to touch/scratch the bearing when removing upper seal.
Good luck, Sir. Ya, getting the one in the block out can be tricky, getting the new one in can be worse.
There's a trick to it, but it's been so long I can't remember what it did.
It wasn't with a Jeep and wasn't the dish-soap thing.
Split seals do have 1 redeeming quality, they're completely captured so they don't just "blow-out" like a one piece.
And I completely agree, just a drip ignore it, they always seep after they've been "exercised".
 
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Bryan

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I plan on working on my RMS (4.0, 2 piece) this weekend. I can let you know how it goes when I am done if you are wanting to fix yours to fix the leak. If it is just a drip, honestly, I would not worry about it. The only reason I am doing mine is because I am burning more oil than I should be. From what I saw on videos it does not look hard, but you will be on your back the whole time and you have to be careful not to touch/scratch the bearing when removing upper seal.
Ya, I'd appreciate you letting me know how it goes. My leak is getting worse. The video I watched on the Jeep Solid channel made it look pretty simple. Thanks for your help.
 

SirDoopYJ

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Ya, I'd appreciate you letting me know how it goes. My leak is getting worse. The video I watched on the Jeep Solid channel made it look pretty simple. Thanks for your help.
Will do. I am referencing Jeep Solid's video as well and this How-to write up from the TJ forum:
 

SirDoopYJ

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Unfortunately, I did not get to my RMS this past weekend. I had alot of trouble working with my transmission to get it's gasket changed.