This morning i ran it in 3rd all the way to work. I was at 2400 rpm's with the speed o saying 58, but with the over size tires, I am sure I was doing 65

So with that info, would I be saving gas using 3rd all the time vs OD? In OD i normally run 1800 rpms at the same speed but every small little hill it drops gears and shoots up to 3 grand.

 

I average about 11-13 city and 15-17 highway on 31's and 3in lift. I drive rough so that explains the low milage, also I dive around 75-80 on the highway.

 

also, i see you're running steel wheels. the steelies that i looked at weighed 33lbs. the alloys that i bought weighed 17lbs. that saved me some weight. makes a big difference in gas mileage.

 

The Jeep 4.0 doesn't reach it's peak HP until approx 4600 rpm and peak torque until 3200 rpm. This has always seemed high to me, I think the 4.2 ltr engine reached peak torque around 1800 rpm.

My 4.0 does not reach RPM much higher than 2k rpms. I have had it around 4k rpms and it felt like it had good power, but man was it screaming.

When I drive (granted it is a stock XJ) I keep mine at 1500rpm when cruising. I shift between 1800-2000 rpm. I am already in 5th when I hit 45mph..

 

btw, if you're gonna keep driving in 3rd, you're gonna need to upgrade your tranny cooler. and also, the most aerodynamic speed for the XJ is about 55mph.

 

x2 i get the best mpg between 45-55

 

That's what I am getting right now. I was told by many to change the O2 sensor in the exhaust...Tj