Holy crappp, 80 mph!!! How much in gas did you pay for on the trip?

 

Stock tires and no lift on the jeep at all. The speed limit was 70 and the jeep felt great at 80 smooth as can be. What was really funny was the mileage went up when I was in the mountains of tenn and Kentucky it makes no sense at all

 

you answered your own question, slow down! 80 mph is going to get crappy mpg on any vehicle.

 

I've always found a sweet spot on the highways with my Jeeps around 60-65mph. Nets the best value of speed and economy. It sounds like with your speedo inaccuracy you may have been going 20-30 per that.

Nearly every truck-style vehicle will have huge efficiency reductions at 75+ mph and 80+ is well into a very inefficient range.

 

Head wind probably played a factor in it. I get around the same mileage as you described in my 2011 j/k. I have a 3.5 rc lift, custom front and rear bumper w/tire carrier and full roof rack. Winch. Stock 32" bfg's

 

I get around 20 mpg but I drive 65maybe 70.

 

I get around 13-14mpg and I'm on a 3" with 35s and I cruise no faster than 70. The Rpms are around 2000 at 60-65. I switched to my soft top, but I wanna say I get better mpg with my hard top on

 

Guys, this is the original poster. Someone else posted that their Jeep was lifted. The original poster DOES NOT have a lift or big tires.



3.8L engine...what trans? What gears? Tire size? How many miles?

All that plus you're driving too fast. The percentage increase in power to go faster and faster is almost exponential past like 60mph. You're burning a lot more fuel to go 10mph or so over the limit.

 

That's real bad for a stock Jeep. Any chance E85 was used at any point? And was regular fuel used in Tennessee and Kentucky?

 

2011 JKUR, manual, and 4.10s here. 80mph is the culprit. I went on a trip from France to Germany, but that was only part of the trip. It is about 267 miles. On the way to Germany I did mostly 80mph. Had to slow down to 70mph to make it on 1 tank of fuel. I barely made it. I got about 275 miles (about 12.5 mpg) out of that tank. Fuel guage was on "E" for 10-15 miles. I was running on fumes. For the trip back, traveling the exact same route I did a max of 70mph. I got about 380 miles (about 18.5 mpg) out of that tank. I did the calculations the old fashion way. I know my computer is almost 2 mpg off so I don't look at it. I also kept it in the ECO range (yes mine actually works correctly!!!) as much as possible. So doing 80mph is what caused the poor gas mileage, as well as a lead foot to get to 80mph!