15w-40

[UnlimitedLJ05]

Does anyone else use 15w-40 in their 4.0L? Both my 98 and 05 run much smoother and qeuiter especially in the summer months with it. I know outside the US its spec'd for 15w-40. I think the tree huggers kept it down to a 10w-30 in the states for emissions. 10w-30 to me though is much to light for a well broken in 4.0L. I found the Premium blue or delo to be the best for them.

 

[PoliceMonkey161]

Try adding some Lucas Heavy Duty Oil Stabilizer as well! Keep in mind, if you live in a climate that has below freezing coniditions in the winter, this oil weight is not the best choice for cold starting..... I use it in manual trans, diffferentials and T-cases. Of all the product that have hype, their's actually works. It even brought new life to my busted up riding motor, no I don't mean a "Suzuki Samurai" :lol:

 

[superj]

i have 15-40. it noisier with this grade oil then the 30w so i am going to go back to 30 or 10-30

 

[JohnnyO]

Since you live in Texas you shouldn't have to worry about the 15w-40 in cold weather. When it comes to oil, the only way to know for sure is to get a used oil analysis (UOA). I use Blackstone Labs, costs $25. Blackstone Labs
It is perfectly okay to use a diesel-spec oil in a gas engine, especially on older flat-tappet Jeep engines. If that is what you have then you should run either a diesel-spec or high-mileage oil for the extra zinc they have. I tried Rotella T-5 10w-30 once in our Jeep, the UOA was fine but oil consumption was insane. It burned 4 quarts in 3000 miles...it only HOLDS 4 quarts...probably why the UOA was so good, LOL. I went back to Max Life 10w-30, UOA was fine and it burns less.

 

[superj]

I have the rotella in mine. It actually has not lost any oil on this oil change and it normally loses a half a quart every couple of fuel ups.

I used a larger ford oil filter for extra oil in the system to help with the oil being cleaner. I don't remember how much this jeep holds but it was a lot