Top Ten List - Maximum MPG

[Hillbilly XJ]

I guess trade your XJ for a Chevy Volt, then the mileage will increase.

On a serious note I did have a mileage increase when I changed gears from 3.55's to 4.56's. I do have 33x12:50x15's and the old gears caused the trans to go from OD to Drive all the time almost on level ground it seemed.

I have a lot of extra weight and other things that cause drag, last time I filled up the mileage was 15.8 and I was pleased. Much better than the 12 mpg before.

 

[kastein]

Keep your tires filled.

Most importantly... KEEP YOUR FOOT OUT OF IT.

I hit 23.13mpg in my MJ once. Summer gas, highway tread 225/75R15 tires, stock 207k mile 4.0/AW4, 3.55 gears, all highway miles, and a severe hangover that made me extremely unwilling to accelerate, decelerate, or push the gas pedal hard enough to make any more noise than I had to. 55-65mph the whole way... with 3/4 ton of cargo in the back, on i84 through Pennsylvania, NY, and Connecticut.

I hit 22mpg in my XJ on 235/75R15 tires, 240k mile 4.0/AW4/NP231, 3.55 gears, doing 80mph on the mass pike, regularly last fall. Summer gas and maintained my speed without much braking or acceleration.

Keep your manifold vacuum up (i.e. less throttle) and maintain your vehicle. New plugs, wires, cap, rotor, and air filter can't hurt. If it's throwing any codes, find out what they are and fix it, because some of them severely affect your fuel economy. Higher manifold vacuum = less air going into the engine, means the ECU will aim for the same AFR and also put less fuel in. Now, if it means more RPMs because you have to drop a gear, that's going to affect things somewhat, but the point remains.

edit: make sure your engine is running at the right temp, too. If you put a low temp thermostat in it or have a stuck thermostat and you're running at or below the 180-190 degree range all the time you'll never enter closed loop and it will suck gas like none other. Toss a new 195 degree Stant SuperStat in it and leave it alone.

 

[genevamotorsports]

These are low compression engines. Make sure to use the lowest octane fuel you can without the engine pinging, which should be 85-87. The lower the octane, the higher the BTU output of the fuel. High octane fuels are only good for high compression engines. It's a small amount of mpg but it helps the wallet too. Make sure your engine is in good tune to prevent detonation.

 

[markaboo929]

My usual mileage is between 18 and 20 mpg hiway.I am running 4.6 stroker,stock 3:55 gears,auto 2 wheel drive,235/75-15 BFG Rugged terrains '96 XJ.Speedo is dead accurate..adjusted with correct gear,GPS verified.I just discovered that a Marathon Station near me has 87 NON-Ethanol gas.Funny thing is right now reg 10% Ethanol 87 is 3.58 per gal...NON Eth is $3.50!!!I just installed a 63 mm T Body and I will be watching my MPG closely now.