Hello all. I am in need of some opinions / help. I bought a 1997 Wrangler TJ SE with only 60,000 miles a few months ago. I love the Jeep, and have had a lot of fun driving it. Here's the problem. I have figured the gas mileage of my Jeep over the last 5 or 6 tanks of gas - and the results are not good. I am getting about 8 to 10 (if I'm lucky) MPG out of my 4-banger. It should be getting 18/20 MPG. I drive 60 miles to work each day, so the 8 MPG just isn't going to cut it. I don't hot-rod, red-line it, or put it into 4-Wheel when driving highway miles. What could be going on? I have replaced the Cap, Rotor, Plugs, Air Filter, dumped a can of Seafoam in the gas, cleaned the throttle body...and nothing is working. Any help you guys could give me on this would be much appreciated. Thanks so much, AC.

I have two questions.
1. Did you attend public school?
2. What size tires are on that Jeep?

Eight miles per is almost out of the question. Do you fill it completely and mark the miles (or use a trip meter).. Then fill it at the same pump next time?
Where do you live? Is it very hilly?
Again what size tires are on that ride? And any engine modifications?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

1. Yes. I was learned in the Eldon Public School District.
2. 31x10.5x15

I fill it completely and mark the miles with the digital trip meter. I live in Missouri. Not really many hills. No engine mods - it is stock. I know - I don't understand it either. That is why I checked over the course of 5 tanks of gas. Thanks for the reply. AC.

did you have your spedo corected for the oversized tires?

nope. didn't have anything altered with the larger tires. could that cause it to be 10 MPG off though?

Well your tires now are ~11% bigger, so your spedo and odometer are also going to be off by that amount. Personally from what I have heard, I think your 18-20 MPG is a little high for lifter wrangler with a 4 cyl.
Have you checked your compression?

Ac that public school will do it to ya every time won't it?
I would believe 12 mpg from big tires and lots of gear changing.8 mpgwould have black smoke trailing behind you.. and prolly lights blinking all over your instrument cluster.
Why not give your next tank a try and get a calculator you can take with you to the gas station?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

well 31 inch thires aint that big speedo will be v a little off what gear ratio u running

This has been mentioned before, but let me recap a couple of factors:

(1) If you installed larger tires on the jeep, but didn't change your speedometer gearing or calcualtion, your speedometer is going to still be calculating miles based on the turns of your axles. However, those axles are now turning larger tires, which are covering a greater distance with each revolution than the old tires were. For example, if the original tires were 27", and you now have 31' tires, that's an increase of about 15%. So, if your odometer says you traveled 100 miles since your last fill-up, you have actually traveled about 115 miles. So, if your mpg calcualation comes out to 10.0 mpg, it would really be 11.5 mpg.

(2) Four cylinder engines are very inefficient if run at lower-than-designed rpm's. If you didn't change your differential gearing when you installed the larger tires, you re running that 4-cylinder engine at an rpm that is about 15% lower that the engineers designed it for. That means it will get poorer gas mileage.

(3) I think a figure of 18-20 mpg is pretty unrealistic for your Jeep. Even with the proper change in differential gears, and a speedometer gearing change, you are driving a fairly boxy Jeep that is now sticking up in the air higher than OEM, and thus catching more wind drag -- that will lower your mpg considerably.

question, previous owner had 35's on the jeep but changed them to 33's before he sold it, i highly doubt changed the speedo gear but when i was driving it home i called my dad and asked him how fast he was going and he said 65 and the my speedometer said 65 but the other day when i was driving down the street the police had one of there things up that tell you how fast youre going and it said i was doing 30 when my speedometer said 25, any possible chance the police thing was off? or was my dads car off, his car still has the stock tire size