Which saves gas: driving with windows down w/ no A/C or A/C and windows up

Gas here in Hawaii remains at $3.07 and up, sometimes dipping to $3.00 so looking at ways to stretch gas mileage. I've been told that driving with your windows down (A/C off) produces drag causing the vehicle to burn more gas to compensate for the add'l drag. It's also been noted that driving with the windows up reduces drag but the A/C has to be on as it will get too warm in the truck.

Dumb question but anyone know for sure which is best on gas? Tracking my miles/gal, I'm getting close to 15 miles/gal with mixed city/hwy use, mostly city, A/C off windows down most of the time... I have a bed cover to help but seems I can't do any better than 15mpg...

Aloha, driving habits have the greatest impact on mileage. All being equal, at 65 mph windows up and no a/c (vent & fan on) verses a/c on I loose approx. 1 mpg w/cruise.

Punch,

Windows open causes more drag, however, at speeds below about 40MPH the primary source of drag is rolling resistance, not air resistance. So, if you are doing primarily city driving, you are not going to notice much improvement in MPG with the windows up. Highway driving is a different matter. In that case, windows up with the AC on is the best combination for higher MPG. Windows up with no AC should be better still.

this was an episode on mythbusters.........however I did not watch it.

my guess is: its a wash, so why not enjoy some nice dry a/c? (plus its not as noisey/smelly with the winows up)

Check the Mythbusters site. There was an mph where it made a difference, but I don't remember exactly (maybe the same as already posted).

I saw the episode on Mythbusters. The Ford SUV (Expedition I think) driving with the windows down achieved 15% better mileage than the exact same vehicle driving with the a/c on its highest setting. The vehicle with the windows down made thirty more laps than the a/c-using vehicle on five gallons of gas. I think it was a one mile track. The computer predictions for the test were the exact opposite, but real-world driving once again proves hypotheses incorrect.

Road and Track magazine within the past year said that the engine power lost to A/C (and the fuel to supply this engine power) costs more than the aerodynamic cost of open windows. They estimated that the typical A/C compressor uses 7 HP to run it. At a steady speed, 7 HP is a big percentage of the power supplied by the engine to keep the car moving.

Dumb question but anyone know for sure which is best on gas? Tracking my miles/gal, I'm getting close to 15 miles/gal with mixed city/hwy use, mostly city, A/C off windows down most of the time... I have a bed cover to help but seems I can't do any better than 15mpg...
I primarily drive with windows up and with automatic climate control on (I bought it to use it). My driving is mixed city/hwy and after 31,500 miles, my overall non-towing figure is 19.28 mpg. I don't think the AC/window dilemma is the major factor in your mpg figures. Since you drive mostly city, that probably is the major culprit.

I think your best gas mileage would come with the A/C off and windows up. :D

I was just going to chime in - the best condition is with the windows closed and a/c compressor off. Opening the sliding rear window dramatically improves the air flow in the cabin - but does not affect the aero significantly. This is a good alternative to sweating and saving gas.

There was an article in Car and Driver within last two years, saying that with windows down and no a/c gas mileage was slightly higher (less gas consumption) than with a/c on and windows up. It wasn't a big difference and they tested it on 3-series BMW. I would think it all depends on the vehicle's aerodynamics. The results may be different for RL.

I often drive with the windows up and cycle the AC by turning the compressor on only when the cabin needs to be cooled down. I often wondered when the climate control temp is raised if the compressor cycles off more or just mixes in warmer air.

OK............flame me everyone, but seriously I can't help but ask. Not trying to be a smart a**, but how far and how fast can you drive in Hawaii nowadays? I was there years ago and you couldn't drive faster than 45 mph. I could drive around the entire big island in 4 hours or so. I figure the difference would be negligible since you're never going too far and never getting up to cruising speed where your RL would get the best mileage. ???

If it's hot out, use the AC. If it's cool out, roll down the windows. Not to be a jerk or anything, but is 1-2 mpg worth being comfortable? We've all paid pretty good prices for our trucks so I'm making the assumption that most of us are doing ok for the most part.

Again, not to be a jerk, but be comfortable. By the way, I gassed up here in NE at $3.14 for regular unleaded.

but be comfortable

hmmm Sometimes I drive with the windows cracked down just a bit, sunroof open, back window open and the AC on !!

Is that comfortable?? to me it is....

:D

IMHO, there's no hard & fast answer to this Question of the Ages.

Windows up, A/C on = lower gas mileage.

Windows down, A/C off: suction that creates drag on vehicle= lower gas mileage.

Open truck bed = drag causing lower gas mileage.

Keep the engine tuned up, tires properly inflated, drive responsibly and you'll have better mileage than most. Happy Motoring :cool:

Open truck bed = drag causing lower gas mileage.
Actually, this is incorrect, unless by "open truck bed" you mean driving with the tailgate down. MythBusters challenged this myth as well--open bed pickup truck, tailgate up vs. tailgate down. With the tailgate up, air flow over the open bed creates a "locked vortex flow"--basically a large constantly rotating "bubble" of trapped air--in the bed of the truck, creating a smoother flow of air over the truck. With the tailgate down, this vortex doesn't exist; airflow is directed down the back of the cab and onto the bed, creating more drag and, in effect, lowering gas mileage. (BTW, a tonneau cover creates the same amount of drag as the bed with the tailgate down.)

As far as windows up & A/C vs. windows down & A/C off, they determined that below 50 MPH it's more fuel efficient with the windows down and the A/C off; above 50 MPH, it's more fuel efficient with the windows up and the A/C on.

Ok here is my $0.02 worth roll up all windows, open the drives door, get out, and walk!!! If you are luck enough to see a sprinkler jump in. You will save a lot of gas and maybe lose a few pounds:D
p.s. this will also help from getting that musty smell from running the a/c, save you lost of big bucks