Ok, so I did a test to see how much the top down impacts mpg. All miles were typical to/from work, 100 miles each day with 85 being on the freeway. I ran a full tank using the a/c and averaged 23.8 mpg. Then a full tank with the top down and averaged 20.9 mpg. I new top down would be worse but 3 mpg was more than expected.

 

I get 20 with my hard top and doors on and 18.5 with it all off but that. Lil difference is totally worth the freedom feeling of a naked jeep

 

I'm running no doors and top down, and as of the last fill up, I'm getting about 15 mpg. And for the freedom I feel, and the compliments my jeep gets... For example yesterday someone was like,"holy crap, you can take this anywhere can't you?" "Yeah, just about. Have fun brother man."

Totally worth it.

 

Who buys a jeep for its MPG?

Seriously though, its even been shown on mythbusters just how much of a difference the windows up with AC on makes. They found (as well as others) that its typically around 45mph constant cruising speed that the difference begins to occur. Anything slower than that, or with stop and go, and the AC will use more gas due to robbing power from the motor. Higher speeds you begin driving a parachute with the windows down as the air sucks into the cab. It would be better if the tailgate had more airflow, or a deck lid... but it doesnt.

 

I've never believed in the A/C effecting the fuel efficiency unless it's in an old car or one with an engine that is WAY too small for the vehicle. When I was in high school and gas was close to $5/gallon I saw people driving with the A/C off and windows down when it was 115 out. Of course they said it was "to get better gas mileage." I don't think they realized that it didn't help, and if they really wanted to get technical, wouldn't rolling the windows down create more drag therefore lowering efficiency?

Not trying to take anything away from the OP, the test is still interesting of course. But like CoreyZ said, who buys a Jeep for fuel efficiency? I can understand trying to drive as efficiently as possible, but since my JK maybe get 14-15MPG on the freeway (17 in really flat areas while doing 68) I just deal with it when I drive it, and I have a small truck for when I don't need the Jeep.

Heck, I just took the JK to Vegas and back 2 days ago and averages 15.3 there are back doiung 65-72MPH average. It's not great, but for a lifted brick I'm not upset. I'm, sure I know I could have done 80MPH, but then I'd be getting aroind 13ish MPG. I had the hard top on, A/C blasting, and took my time in the right lane with the seat tilted back and the cruise control on.

 

I find the best combination is top up, doors and windows off. I average 19-20 with the door and windows on and 21-22 with the top up and the rest off.

I beleive this still maintains some air flow around the Jeep, but I lose the weight of the doors.

 

I do agree that we did not buy the JK for its fuel economy, I only got 12 mpg on my built TJ. This test represented my first 2 tanks of gas on my new 2012, I was more or less just getting to know my new ride, playing with the new feature of an mpg readout, and there are many threads on the subject so what's one more.

 

With the top up and windows on, you have a stream lined brick. Windows down top off, you have a less stream lined brick with lots of drag. I don't really see any surprise there...

 

Dont forget that on a brand new engine, it has some break-in left to do. Once the motor is completely broken in (as well as gears and transmission), then you will start getting a more solid reading on your MPG and can experiment with different things.

If you can, lose the rear seat. Then strip out any unnecessary items as well to lessen the weight of the Jeep. Things like hood screens (the bug deflectors) can actually help you with aerodynamics as well by lifting the air up before it hits the damn near vertical windshield.

 

I've never paid attention to the gas mileage really, but interesting.