Hello, i just purchased a 99' xj with the 4.0 and i was just wondering what everyone was running for oil wieght and brands? are any of you running the full synthetic 5w-40 oils? shell rotella t6 or the scheaffers 9000 series 5w-40. Thanks, Mitch

 

Oh no....

 

 

I run Valvoline SynPower full synthetic 10w30 in my XJ. It's good stuff, you can go farther with fewer oil changes, and my Jeep runs great with it.

I've ran synpower in everything I own for years actually.

 

well mine has 139k on it now and im not shure what was ran in the past so would you say i would be safe to switch over to synthetic.

 

The back of the Synpower bottle says it is completely safe to switch from conventional.

If your XJ has 139k on it, I'd recommend running Valvoline's High Mileage Synthetic 10w30. It has more detergents in it to clean the engine more effectively.

 

Thanks for the info, i'll check it out this weekend

 

Lol hell yeah Synpower for the win I took my valve cover off today omg I got so excited i had an accident it looks like the motor is brand new.

Valvoline Synpower 10w-30 hey they garanty 300,000 miles and the 4.0's are already solid motors

 

Look at the owner's manual

 

Quakerstate high mileage 10w30 or 5w...depends what they have, usually one is sold out. Runs like a champ!

 

for summer time; how about using 10-40 on 4.0 ?

 

According to the owner's manual 10W30 will be fine for temps down to 0*F to beyond 100*F

 

I run Mobil 1 5W ( or any other good synthetic oil-Castrol-Penzoil) in Winter and 10W in the Summer with a GOOD filter.

No problems -good oil pressure throughout RPM range. Sits at about 20- 25psi @ idle and 40-60 in the higher RPMs

 

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Sarcasm? Anyways, I'm running rotella 10w-40 in the summer.

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