Does anyone have tips for increasing gas mileage?

[Rubicon88]

Terrain you drive? Flat or hills? Around town or hwy? If you've a heavy right foot your mileage is in trouble no matter.

If you're traversing a ton of hills that high gearing is killing you.

For optimum mileage at cruising speed the target is around 2k rpm. The more you cruise over 2k the more mpg you will lose.

If constantly trying to set a speed record 0-60 your mpg will suffer.

 

[Jackjack97]

Your engine is slightly lugging/operating very inefficiently at rpms that are lower than optimal for even 31's. Raising your rpms by regearing your axles should increase your mpg. Mine went from sub-12 to around 14.6 after regearing my axles to raise my rpms up to where the engine operates more efficiently. Lower rpms like your 3.07 axle ratio is causing does not usually mean better mpg.

Also, make sure your tires are properly inflated, I'd be at no less than 31 psi for your 31's.

The last mechanical problem that will cause reduced mpg is a bad upstream O2 sensor. They go bad just like spark plugs do and a bad upstream O2 sensor could be erroneously telling the computer your fuel mixture is too lean which would cause the computer to set it richer. Since a defective upstream O2 sensor would never tell the computer the mixture is correct the computer would keep raising the amount of fuel sprayed until the mixture is full-rich which will destroy the MPG. But your present sub-12 isn't so bad that I'd suspect that.

The 3 things I'd try are 1) Slow down. 2) Make sure your tires are properly inflated. And if $$$ is not a huge issue I'd regear your axles to a more appropriate ratio like 4.10. Not only should it help your mpg, it would provide a dramatic (!!!) performance boost. Your TJ is a dog, performance-wise, with 31" tires and 3.07 gearing.

Yep i currently have a Dana 44 sitting in my garage with 3.73 gears im going to be swaping in with some free 3.73 gears for the front this is not ideal for 31s but its dang near free and I will be going to 35s and be regearing to 4.88. the o2 sensor would make sense because the jeep smells like it is dumping fuel sometimes.

 

[Jerry Bransford]

the o2 sensor would make sense because the jeep smells like it is dumping fuel sometimes.

That's an astute observation, that's a symptom of the fuel mixture being too rich which can be caused by a defective upstream O2 sensor. If you replace it, make sure to ONLY use an NTK sensor and make sure NOT to use a Bosch O2 sensor which doesn't work right in our Jeeps for long.

 

[Rubicon88]

Yep i currently have a Dana 44 sitting in my garage with 3.73 gears im going to be swaping in with some free 3.73 gears for the front this is not ideal for 31s but its dang near free and I will be going to 35s and be regearing to 4.88. the o2 sensor would make sense because the jeep smells like it is dumping fuel sometimes.

Don't forget you'll need a new carrier for the front unless you install a new true locker replacing the carrier.....

 

[jjvw]

Ever since I put 35s on I’ve never got better than 10-13 mpg.

Mine is pretty consistent at 13-14mpg with 35s

 

[cpwolf]

For optimum mileage at cruising speed the target is around 2k rpm. The more you cruise over 2k the more mpg you will lose.

This is very different than what I've been reading all over this forum. Cruising RPM about 2,700 or slightly higher I've read over and over. Running our 4.0s at 2k rpms I've read repeatedly that is too low, the engine is not running efficiently etc.

Hmmm.

 

[Lou]

For optimum mileage at cruising speed the target is around 2k rpm. The more you cruise over 2k the more mpg you will lose.

crap I guess I can only go 40 mph now

 

[Irun]

Re-gear
Do a tune up
Replace O2 sensors
Keep a light foot

Even with all those, don't expect to get any dramatic results. It's a square box with horrible aerodynamics. However, it's the funnest brick you'll ever drive!

 

[Jramos013]

this is the best we can come up with to get a better mpg:
https://wranglertjforum.com/threads/tired-of-that-bad-mpg.42917/

 

[AndyG]

You can get up to a month out of a tank of gas if you just won't drive it.

Maybe longer.

 

[Alex01]

I typically get around 12-14mpg with 35" tires and 4.88 gearing @25psi.

I gained 2 mpg by putting it on a trailer though.

 

[Jerry Bransford]

This is very different than what I've been reading all over this forum. Cruising RPM about 2,700 or slightly higher I've read over and over. Running our 4.0s at 2k rpms I've read repeatedly that is too low, the engine is not running efficiently etc.

Hmmm.

His comment that going over 2000 rpms at cruising speeds produces lower mpg is laughable to anyone with any experience. Sure 2000 is perfect for my wife's Lexus and my Genesis but it's not what our Wranglers require for larger tire sizes. My TJ with 42RLE and 35" tires was cruising at somewhere around 2250 rpms at 70 mpg with the 4.88 gears it came with. Its performance and mpg sucked, it never got better mpg than in the upper-11's. Regearing to 5.38 brought its rpms up to around 2500 at 70 mpg and everything got better... it performed better and my mpg increased over 2 mpg to 14.6 on the highway. Over 2.6 mpg better by raising the engine rpms from having regeared from 4.88 to 5.38. If I could without having to replace my lockers I'd go even deeper than 5.38. Its current rpms are barely adequate, a couple hundred more like I had on my previous TJ would be much better.

 

[Fishtaco]

I get 15-16mpg (220-250 miles per tank) with 4.0l, 6sp, 3.07, and 31's. Oddly, I get better mileage in it than my wife does, and I shift about 3-4k RPM, and she shifts 1.5-2k RPM.

This was my problem i was shifting at too low RPMs and since I have raised RPMs I get better mileage?

 

[Fishtaco]

I also shift around 3-4

4 seems a bit high to me?

 

[Artsifrtsi]

This was my problem i was shifting at too low RPMs and since I have raised RPMs I get better mileage?

Shifting like that, you’ll stay in the power-band, and not work the engine as hard

 

[Viking Jeeper]

4 seems a bit high to me?

me too

 

[jjvw]

4 seems a bit high to me?

I shift above 3k and often well into 4k.

 

[Artsifrtsi]

... or you can buy a Prius...

 

[Rubicon88]

crap I guess I can only go 40 mph now

4.88 or 5.13?

 

[Zorba]

4 seems a bit high to me?

Same here. I usually shift around 2.5 with a light foot, 3 if I'm in a hurry, 3.5 if I'm in a panic. Give or take, I usually go by engine sound.