Iv noticed Iv got better mpgs this week driving around in 3 instead of D. Iv been driving the exact same as usual. I have a set of 30" pro comp at's with 35psi in them. I have the AW4 trans NP231 tcase with the 4.0 if it helps any. What would cause this? Is my trans on its last leg?

 

Your only reason for assuming your trans is going out is because of better gas mileage?

 

Your xj is most fuel friendly around 23-25krpm... I just recently installed a vacuum guage in my jeep so that's why I know this. So when your trans is in "3" rpms are a tad higher, probably somewhere in that 23-25krpm area when cruising. Thus better gas mileage. Your trans is fine.

 

Figured my overdrive band was going out. I had a truck a few years ago that would eat gas in overdrive cuz the overdrive band was wore out.

 

Wow really then why the heck do we have overdrive then and is it gonna kill my trans to run it in 3 instead of D?

 

The larger tires have changed the final gear ratio. It take more power to turn the taller tires. As you found out the Jeep is more efficient with your driving style in 3rd instead of OD. Have you adjusted the speedo for the tires? This will add to your MPG.

Ron

 

No I havent adjusted the speedo sense it is dead on the money. I just find it odd going a size bigger would make that big of a difference

 

X2?

 

It's not going to kill it by running it in 3. Alot of people with oversize tires and stock gearing do this. The aw4 is a pretty tough trans.

 

Thats good to know Ill just lock it in and let it ride at least it saves me fuel lol

 

Well this is odd I have been getting really good mpgs running 3 in the colder weather but this week has been really warm like 60-80s and my mpgs have dropped yet again :/ I cant seem to win here