[Mike46280]

Hey everyone. Just bought my 2006 Wrangler with 41000 miles. Was really happy when I bought it 5 days ago but now I struggle trying to improve the gas mileage. May not help that the dealership put the wrong size tires on it. 2" to small. and over an inch narrower than the proper size. 1st gear in this 6 speed jumps to 3000 RPM really fast. I love Wranglers they are great vehicles but my 91 got better gas mileage than this 06. I'm hoping to resolve all of this by Monday when I take it back to the dealership for service. Could the tire size be the cause of the high RPM and the bad gas mileage. I'm getting 10 MPG right now when I should be seeing at least 15. Has anyone tried anything that has worked? I will be cleaning my Mass Airflow today. Hope I get to keep this one I have always loved the 4.0 L6. Any advice is appreciated. I don't want to take my Wrangler back. But I can't handle 10 MPG in my daily driver.

 

[00silverTJ]

What size tire's are on it?

What size tire is indicated as the factory size on the door jamb sticker?

 

[Mike46280]

Size on door sticker is 30x9.50 but dealership put a P235/75.

 

[racefan88]

You Don't need to use 1st gear when starting on the street I run 33" tires and never use 1st except off road. Cleaning your TPS, check your plugs and a fresh air filter are a good place to start.

 

[00silverTJ]

how are you checking mileage?

 

[Water Dog]

Upping your tire size would help on the gearing issue, but not sure how much benefit gas mileage-wise it will make. I would probably put some 31's on it, if it were me.

 

[BM3]

Wouldn't having the incorrect tires with his gearing affect the odometer & speedometer?

 

[Mike46280]

does affect the odometer and speedo. about to see how much. Heading to my dads to use his garage for some sensor clean up. I'm checking mileage with simple math. At last fill up my odo read 141.7 miles and I put 13.412 gallons in. 141.7/13.412=10.565miles. How ever the odo is not right because of tire size.. HMMMM I'm going to kill CarMax. I love my Jeep and I thank all of you for the help.

 

[Digger84]

The 6 speed has less overdrive then either 5 SPd but on my wife's 2004 rubicon with stock 4.11 gears and 33 tires that are really about 32.5 inch diameter with GPS verified speedo and odometer if I drive on highway keep it at or below 65 and rpm in 2200 to 2400 range I can get upper teens for miles per gallon

Significantly less at higher speeds or if run at lower RMP like 1800

 

[JGreen06TJ]

Just for comparison I have an 06 auto with 33's and 3.73 gears averaging 12-13 mpg over the last couple years. 10.5 seems low but expecting high teens seems unrealistic also.

 

[3X4X4]

My 06 auto (Rubie) with the 33 inch tires does indeed get over 15 MPG+. I am 62 yo and drive like a mature driver and rarely go over 60. Well, from time to time we need to do a little sprint. My speedometer has been corrected for the tires size and my speedometer is dead nuts on. Actually I have set to read about .5 MPH fast. Even more, I was just to lazy to crawl under and do the last tiny adjustment. Yellerbox corrector. I have checked it with both GPS and timed over a mile.

So, my fuel economy is accurate, the OP, you need to correct your speedometer for your tire size, which I would not do until you get the tire size on it that you want to run.

Smaller tires would show more miles traveled so your MPG should be high and speed is lower than actual. Larger tires show less miles traveled so MPG should be low and speed is greater than actual.

Tuneup, plugs, air filter, O2 sensors, fluid changes (synthetic), air pressure, mature foot on go pedal = good MPG.

J

 

[Shark_13]

If the tires are a different size, then the speedo is off and so is your odometer. Therefore your calculations aren't accurate.
Depending on your location, you could still have winter gas which generally gives worse milage.