Gas mileage: A/C versus Windows down

[MattHamilton]

A long time ago someone told me running the A/C with windows up gets better gas mileage than A/C off and windows down. I completely understand one of the objectives of owning the JT is the convertible, and I actually love the roof off as well. And I also understand the JT is never going to get "good" mileage. But I'm just wondering if anyone here has ever actually measured; and if so is the difference significant, especially over a longer drive.

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[WXman]

I believe Myth Busters tackled that question once and discovered that it depends on speed of travel. On the interstate, A/C was more efficient due to higher wind drag. Below 55 MPH or so, windows down was more efficient because the wind drag is low and you're not forcing the engine to turn the compressor.

Personally I keep the HVAC off as much as I possibly can year-round because I just hate being sealed up in a box.

 

[JTBurns]

Agree with above, definitely depends on speed. I've noticed my mileage goes down with the front doors off, but the back doors and roof are still on, which can't be very aerodynamic. I wonder if naked gets the best mileage?

 

[Papa Jawa]

A long time ago someone told me running the A/C with windows up gets better gas mileage than A/C off and windows down. I completely understand one of the objectives of owning the JT is the convertible, and I actually love the roof off as well. And I also understand the JT is never going to get "good" mileage. But I'm just wondering if anyone here has ever actually measured; and if so is the difference significant, especially over a longer drive.

Unfortunately I drive fast, with the windows open and a/c on. 14-15 mpg.

But my JT is not really for just “transportation.” It is also my therapy, my joy, my fun and my peace. I feel good when driving, and I can go just about anywhere I want. Mostly I want to go where there are no people so I can enjoy my therapy, my joy, my fun and my peace.

I chalk the extra cost of fuel to paying for the other stuff. My last car was a civic. I was mostly grumpy in that.

 

[AverageDad]

Agree with above. Drag isn’t much of a factor at low speeds, so windows down would be better than AC. At high speeds, AC would likely be better - or at least as good - for MPG.
windows down with top on will create drag at speed as that wind gets pushed into a box. Going naked will reduce drag as the wind can flow right through. It still won’t be as clean as flowing over an enclosed structure but probably better than AC.
If you want ultimate MPG, drive slow with AC off and windows up. But, I wouldn’t recommend it.

 

[foo.c]

I doubt the difference is enough to worry about when driving a brick.

 

[NateKY]

Agree with above, definitely depends on speed. I've noticed my mileage goes down with the front doors off, but the back doors and roof are still on, which can't be very aerodynamic. I wonder if naked gets the best mileage?

Going naked dropped mpgs on my 2020 Gladiator. Went from 18-20 down to 15-17. Not saying this will be the same for everyone, but this was one of the reasons my wife argued about going naked. Lol

 

[redrider]

Comfort is Primary. Mileage is not on my list.

 

[redrider]

Going naked dropped mpgs on my 2020 Gladiator. Went from 18-20 down to 15-17. Not saying this will be the same for everyone, but this was one of the reasons my wife argued about going naked. Lol

Precisely why I generally do not consult the other half-it quickly devolves into an elevated volume, Minnie Mouse screeching discourse on striped giraffes living on the dark side of the moon.

 

[dfwxjer]

I drive a lot of highway miles and have noticed on particularly windy days the mileage drops significantly with the top/doors off.

AC on, top/doors on, and 65-70mph seems to be the best combo for highway fuel efficiency.

 

[brianinca]

Any kind of speed in almost any kind of topless Jeep gives lower mileage. Heck, I have places I have to downshift my YJ from 5th if I want to stay above 70 MPH but ONLY with the top off - the hardtop affects drag THAT MUCH.

As for windows down, when you roll them down and your arm heats up, it's too hot for the windows to be down, mileage be damned.

 

[MattHamilton]

Thanks everyone. I never thought to consider the speed element, but it definitely makes sense to me. I appreciate the time you all put in to this forum!

 

[Fundamental Jeepster]

I got 25 mpg from Des Moines to KC and back with AC on, 70 mph cruise control with my Sport.

 

[ShadowsPapa]

Going naked dropped mpgs on my 2020 Gladiator. Went from 18-20 down to 15-17. Not saying this will be the same for everyone, but this was one of the reasons my wife argued about going naked. Lol

I noticed the same thing - 2.x drop in mpg drop doing exactly the same roads, same driving habits, same speeds.

We have noticed this varies with vehicles - with a Camaro that has a huge scoop shape with windows down we realized a fair drop in mpg - my wife's last Camaro got 27 mpg with windows up, AC on, doing 65-70 and with the windows down, AC off - it was only about 24-25.
The bigger the scoop or sail and the faster you go, the bigger the drop.
It depends on the shape of the car as well as speed.

 

[zach471]

I doubt the difference is enough to worry about when driving a brick.

Just hurling a brick down the highway.

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