Another thing you should know (if you don't already) is that the "mileage computer" in the JK is far from accurate... it will regularly over- or under-inflate your true mileage (usually the former).

I've recorded nearly every fill-up since I had the JK (unfortunately, I lost 2 gas receipts, so have two gaps in my tracking), and will break 10K miles today on the way home from work... My spreadsheet shows a lifetime MPG average of 17+, and there's a noticeable shift in MPG depending on ambient temperature, too. Just another factor to consider.

 

Calculated at every fill I average between 16 -> 18 MPG... Running 35" tires and 4.10 gears in my Rubi.. I do agree we are lacking power yet not much.. If we could get a decent programmer out of Superchips and we could get another 10% -> 15% more power I would be very happy..

 

Sorry to rub salt into this, but my diesel will cruise at 95-100 mph, and still return 24 mph, during running in.
First 2000 miles on clock in 7 days,(Euro Jeep Camp) including 100 miles offroad, and got 24.

Mines an auto, but i believe its the 545RFE, as put on the Grand Hemi, so swapping in a hemi would be easy in europe, but with petrol at £1 per litre, about $1.90 per litre , i would need shares in BP Oil.

 

i have 4.10 gear with 33", still can chirp the rear tires from stop. I'm pretty happy with the engine performance. It's not fast by any mean, but good enough for Jeep. Do i want more power? of course...you can never have enough power =)

 

Part of the problem with putting in a larger engine from the factory is that there would need to be a new transmission put into the Wranglers as our current one is not rated for much power. The tranny that is in there now was in previous Wranglers and has been reliable, and durable. There would be several people upset if they did away with the current tranny.

 

4:10, 6-speed, stock S-pkg Wrangler tires. I get 18 mixed (mostly city), and 20+ highway (as measured by me, not the silly computer). Power seemed weak at first, but gradually improved to quite acceptable about 2-3k total miles.

 

FWIW, most of my daily drive is a few miles at most, never more than a few minutes at a time. I get 13-14 MPG during this. On normal highway/city mix, I get about 17-18, pure highway it's more like 20.

Jeff

 

The Mileage Is Horrible On The New Jk's, I Dont Even Think Im Getting 13. Chrysler Is Considering The Hemi Though

 

With a auto 4.10 my beef is with the overdrive on hills, not power. With od mostly off, I get ~15-17 consistently on my 50/50 driving. With over 11k miles now, my milage has NEVER improved from the first tankfull, and never got over 19mpg... even downhill from Colorado to Texas with a tailwind.

 

Have the front and back Mopar bumpers with the tire carrier and Warn 9.5 i winch in front, total empty weight with full fule, a little over 5100#,s...heaviest Mopar springs in front...have made three long trips with all camping gear and two people so weight would be well over 5500#s... standard transmission...transmission, once you learn ratios, extremely useful in mountains, engine has performed well with plenty of power, torque, off road, very good...off-road the lo-lo is unbelievable...lockers and disconnect make a big difference...highway pickup very good...overall mileage 18.5...the engine performance was much improved after about 2000 miles...now running Magic Purple 5w-20 and use about 3/4 cup of oil in 3000 miles...buy the way, engine capacity is 5.5 quarts...have also changed all other drivetrain fluids to synthetic...have 25 years of experience with the 4.0 in two cj5's and this one performs better...very pleased with this Jeep, absolutely no complaints...delivered January 19, 2007 and did recall for engine stall...