I can get that kind of mileage in my stock XJ also. As long as it is highway driving (with no major head wind). 60 - 65 miles an hour, with the cruise control on. It's the city driving that it eats gas. And my wife refers to the jeep as the "Silver Box"

 

never seen better than 17.8

 

Took this pic Saturday before I filled up. Averaged 19.28 mpg on Shell gas.

This tank had city and highway driving with the AC on half the miles.

It's a 2000 with an automatic.

 

That's funny!!! Best I ever saw was 14mpg. And that was down hill with a tail wind. 2000 4.0 5 speed on 35's and 4.88's. It wheels like nothing else tho. Normal is 12.5-13.

 

Mine is a 2001. Mileage is actually supposed to be better with the air on and the windows closed. A guy in our overlanders group claims he picked up a mile or two per gallon with Neon injectors. Not sure if that is true or it's because he's got clean injectors in. He was right about removing the roof cross bars though. He's also got a diesel liberty that he claims gets 30 mpg on the road.

I did use a on mine. It ran smoother afterward and I think I picked up a little mpg (I started at about 15 last year). Of course the cost of the kit was half the cost of a set of used Neon injectors.

The other thing I did early on was replace the upstream O2 sensor, the one that controls fuel mixture. No code but it was dirty and I think a little lazy.

 

Ive wondered how that 3M kit works. I know just about anything 3M make is quality and delivers but at $40, I'm a little hesitant even being a 3M fan.

Ive thought about changing that sensor on mine too although it isnt too old. Its been throwing a code, and Im kinda thinking it may be the cat....dunno.

 

The upstream O2 sensor controls the fuel mixture and the downstream just tells you if the cat is bad as far as I know. If it's throwing a code on the upstream one, it's probably screwing with your gas mileage. I just changed the upstream two sensors. I have two because all of the 2001's were cali emissions with two upstream and two on them mini-cats behind the header.

I think most jeeps just had a single O2 sensor upstream.

 

I got back from a 5000-mile road trip last week (Georgia to Montana and back) and averaged 23.4mpg for the whole trip.

2001 XJ Sport, 2wd, AW4, 170K miles when I left. All stock except K&N air filter, Dynomax SuperTurbo muffler, synthetic motor and rear gear oil.

Trip was 85% interstates and I never cruised over 70mph. Great trip and the XJ didn't leak or burn a drop of oil, coolant nor tranny fluid despite driving most of the miles through the midwest during record heat waves with daytime temps over 100F everywhere.

 

Just filled up again,61.0 litres did 410 miles since last time = 32.7mpg
Its a 2.5 td 1997 xj.
Pleased slightly better than last time. maybe fuel went down in price slightly