Oil viscosity
- Thread starter Erik V
- Start date
Rubirob
TJ Enthusiast
Seems like the 4.0l “I’m assuming you have this motor” will take any 10w30.. but from what others have said.. stick to conventional, synthetic can cause the rear main seal to leak.. I personally like valvoline.. but any sae verified oil should work great.. just adding to the dynamics of these 4.0l but my 1990 Cherokee xj takes 10w40.. so when I got my 2004 rubicon I was kinda thrown off by the 10w30 requirement.. but that’s what I put in it because that’s what mopar says lol.. I bet 10w40 wouldn’t hurt anything tho.. in a apocalyptic situation you could use it hahaha
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Oh, an oil question......fasten your seatbelts.....
OP
Any motor oil that meets the manufacturer's specifications is acceptable.
The 2006 Factory Service Manual, in the Lubrication & Maintenance section at page 2, specifies motor oil certified by the American Petroleum Institute for gasoline engines with an SAE viscosity rating of 10w30 for ambient temperatures ranging from 0*F to 100*F and above and 5w30 for ambient temperatures from -20*F up to 100*F. There is no recommendation as to conventional, synthetic blend, or full synthetic motor oil.
I don't think there is any objective evidence that synthetic motor oil can cause the rear main seal in the 4.0 engine to leak. There is some support for the belief that full synthetic motor oil can dissolve deposits masking evidence of existing leaks, but the theory that synthetic motor oil causes leaks was debunked decades ago. In any event, the anecdotal evidence on the issue is inconsistent and can be used to support or refute whatever one's personal belief happens to be.
My anecdotal evidence is this: The previous owner of my LJ was using Mobil 1 10w30 full synthetic. There was a minor main seal drip. I switched to Valvoline Maxlife synthetic blend 10w30. The drip stopped. Will the drip stay stopped? No one knows and time will tell. Can I draw any valid conclusions from my observations? No, not really.
Rubirob
TJ Enthusiast
Yea I agree with all of that, I don’t put a whole lot of miles on my Jeep.. maybe 3000-4000 a year.. so conventional works great for me..
I want to say that back in the beginning of synthetic oils they did cause leaks because of the formulas.. but now 20 years later they have improved the formulas so this no longer holds true.. this is just what I have heard tho lol
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OP
Rubirob
TJ Enthusiast
These motors are pretty tough, as long as it’s still running good I wouldn’t worry about the first oil change! Just stick to the 10w30 from now on [emoji106]
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I've been putting 10w-30 in my 4.0 since Dec 10, 1998 the day I drove home from the dealership.
TJ2
TJ Expert
It maybe a little complicated to explain about the particle compositions.
Analogy: Let's say gravel and sand. Gravel is the dino oil and sand is the synthetic oil.
Gravel will not pass through as easy as the sand will do through the tiny cracks.
The leak is stopped by the dino blend particles.
It maybe a little complicated to explain about the particle compositions.
Analogy: Let's say gravel and sand. Gravel is the dino oil and sand is the synthetic oil.
Gravel will not pass through as easy as the sand will do through the tiny cracks
The leak is stopped by the dino blend particles.
In full synthetic high mileage oils they have conditioners that plug those "tiny holes". I am a full synthetic high mileage guy, but I do not push that on anyone. I like it because it has always worked and when I find a good sale I can get 5 liter jug for $25 with a Purolater filter from Advanced Auto. Valvoline Maxlife, like Mr. Bill's referenced works for him and although it is to small of a sample size to tell, but he had a small leak stop after switching.
Valvoline Maxlife is a synthetic blend marketed for high mileage engines. Valvoline Synpower is it's full synthetic line.
I got my TJ about six months ago. Changed all the fluids when I bought it. Bought Mobil 1 high mileage full synthetic. It started leaking a few drops a week from the rear main after that. I then changed the valve cover gasket just to be sure. A month ago I changed to Valvoline regular 10w30 and not a drop since. FWIW.
That's exactly what I run too. I'd only switch to a synthetic engine oil if I lived where the temps get below zero where synthetic does have a legitimate advantage over conventional. I do run synthetics elsewhere like in the transmission & power steering (ATF+4) but I would not in the engine where I live.
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Hmmm , i was under the impression that all 4.0 rear mains leaked.
If they don't leak you better check the oil
If they don't leak you better check the oil
Rubirob
TJ Enthusiast
Same here, Dino for the engine.. synthetic for the transmission and power steering..
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Rubirob
TJ Enthusiast
I use wix 99% of the time.. Napa gold or platinum really but they are wix with a different name.. if I can’t use a wix I go with Mobil one, k&n, Bosch.. just not fram lol.. I have see the YouTube videos of them being cut in half.. no toilet paper for my Jeep/car
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