With the temperature finally rising outside i am wondering which is a better choice on the car.

Is it better to drive on the interstate/highway with:
a.) the windows down and no vents or a/c on
b.) have the a/c on and the windows up

Which one is going to reduce the MPG the least?

 

My guess would be windows down, but you should test it out to see the differences.

 

There was a mythbusters on this a while ago.

http://autoblognews.com/mythbusters-...-down-episode/

 

the original:

MythBusters (season 2) - Wikipedia, the free encyclopedia

revisited:

MythBusters (season 3) - Wikipedia, the free encyclopedia

 

Oh man, I'm all over this one (there's nothing to do at work):

"The fundamental flaw in the MythBusters' test was that the point where the drag becomes powerful enough to inhibit a car's performance with windows down was inside their 45–55mph margin at 50mph. Going less than 50mph it is more efficient to leave your windows down, but going greater than 50mph it is more efficient to use your A/C. Since then, this particular bit of knowledge has been used frequently on Car Talk"

-piper

 

The other thing to remember is the amount of parasitic drag on the engine. I am sure not ALL A/C units are created equal, and i am positive that not every engine deals with the parasitic drag in the same way. There will be a difference from car to car.

 

My SG data says windows up or down at 65 and below have no measurable effect on Eco.
A/C on does for sure.

 

Mental Note taken

 

When I have to have some kind of ventilation in the car and don't want to use A/C I've been cracking all four windows the same amount, usually about 3 inches, to get some air circulation. I don't know how much I'm loosing compared to using A/C, but my SG tells me it's at least a little better than running the A/C. That technique will stop, though, when temps reach over 95 degrees on a consistent basis.

 

windows up, everything off

 

What about AC off and windows cracked with a set of Mugen vent visors? Not too much drag thanks to the design, plus no death by heatstroke.

 

put the vent on, under cool. Just no a/c button.

 

Check this out.

Look at #4.

 

None of the above. The air temperature inside your engine will triger the ECU or PCU to decide how much fuel gets injected. But with the AC on, you'll think that more heat is generated... WRONG. You're going highway speeds so air is constantly circulating in your engine regardless. Rowing down one window down at higher speeds really doesn't do much. The pressure in your car will probably push and pull the air in and out, trying to equalize. But rowing down all four windows is pretty interesting because air comes in the front and out the back faster. Your engine is still taking in the same type of air circulating though the engine. And if that air comes in faster than the engine components can heat up, then you probably won't see a difference in MPG.

 

I wonder if the Fit is like they Civic. I know on the Civic if you run the AC on the lowest fan setting the AC compressor will cycle on and off about 33% on and 66% off i think. So like it'll cycle on for 10 seconds then off for 20 roughly.

Do this after you run it for a while. Make sure the AC has been on for a bit and the car is decently cool inside, keep the windows up and fan on low and listen to the compressor.

 

Based on the testing and SG data I have that does not apply to the Fit.A/C off is always better under 70mph. I say 70 because I have no data above 70 . If you are interested in best Eco, you have no business running 70 or more.

 

The A/C does cycle off and on a lot from what I can tell, and it's not dependent on the fan speed. I was starting to think that it was a mechanical problem, but after hearing this I think it must be normal.

 

I dunno the lower the fan speed the less the compressor runs on my car. Maybe it has something to do w/ a temp sensor and the slower the fan speed the colder the air or maybe the colder cabin air temp the less the compressor runs or something like that.

 

Several studies have shown that windows up and A/C on beats windows down and A/C off. The reduction in drag from windows up appears to outweigh the suposed benefit from no A/C with windows down.

 

Well... here in AZ with the summer rapidly approaching, and temps reaching 115+, I'll be using my AC, thanks.

Mornings usually I roll with the windows down, on the way home from work in the afternoon its AC all the way.