What's less fuel-efficient...running A/C or driving with the windows down?

[NFS4]

I was thinking about this while I was driving down the road the other day. With the A/C on in your car, you take a mileage hit b/c of the extra power required to run the compressor. But would you get an equal hit by driving with your windows down instead...considering that the aerodymanics of the car would be disrupted adversly by air rushing into the car and swirling around in the cabin. Afterall, car-makers shape their cars to have a low drag coefficient and this plays a part in fuel mileage.

Any ideas?

 

[Viperoni]

Originally posted by: NFS4
I was thinking about this while I was driving down the road the other day. With the A/C on in your car, you take a mileage hit b/c of the extra power required to run the compressor. But would you get an equal hit by driving with your windows down instead...considering that the aerodymanics of the car would be disrupted adversly by air rushing into the car and swirling around in the cabin. Afterall, car-makers shape their cars to have a low drag coefficient and this plays a part in fuel mileage.

Any ideas?

highway + AC = good
highway + open windows != good

city + open windows = good
city + AC != good

there ya go

 

[BrunoPuntzJones]

I've seen more than one report on it. Answer has always been "none" (too small to really matter). Remember seeing a guy do it in college and mpg was the same either way.

Linky do

 

[PsychoAndy]

I would say the result is dependent on the car, the engine, the pulleys running the accessory belts and the compressor engineering. I get 30 in the city when its not too hot out with the windows down, however with my 1.6L i get 24 when running the A/C. Thats a signifiant difference. That or my O2 sensor is shot.

I think with a large engine, the effect is there but offset by the fact that more torque is produced. There probably is an effect that is accentuated by small displacement engines.

Perhaps a better idea is a dual alternator config and run the A/C compressor off of electrical current.

Also, do all A/C compressors have a clutch that frees the compressor from the accessory drive belt when not operating?

-PAB

 

[Aquaman]

Well.......... you could do an informal test........... drive one tank with AC on and then the next tank with windows down............ just make sure you drive the same style for both tanks of gas Remember.......... the more times you do it the more data points you will have and you will get your answer

Cheers,
Aquaman

 

[PsychoAndy]

Originally posted by: Aquaman
Well.......... you could do an informal test........... drive one tank with AC on and then the next tank with windows down............ just make sure you drive the same style for both tanks of gas Remember.......... the more times you do it the more data points you will have and you will get your answer

Cheers,
Aquaman

The ATOT way of doing things:

We get Brandon's Camry and get it filled up.

Argument as to which gas is best thread ensues.

Cheapest gas wins. Fill up begins.

Argument as to grade commences.

87 octane is decided. One member dies.

Tank full.

Argument as to definiton of full commences. Also, do we shake the hose and get more gas? Do we stop when the handle stops? Do we top off? If so, when? Next dollar, quarter or nickel?

Everyone then gives up. I like research ATOT style!

-PAB

 

[SyahM]

Originally posted by: Aquaman
Well.......... you could do an informal test........... drive one tank with AC on and then the next tank with windows down............ just make sure you drive the same style for both tanks of gas Remember.......... the more times you do it the more data points you will have and you will get your answer Cheers, Aquaman

LOL, yeah, you try that and let us know the result ... also, it'll be great if you can sample it using many different cars

 

[gopunk]

what if you just opened the vents? no disruption in aerodynamics, no ac, relatively cool (provided you're moving fast)

 

[Evadman]

I get either horrable gas milege or hjorrable gas milege, so what is the point?

<--- drives with windows down and A/C off.

 

[amnesiac]

Originally posted by: Evadman
I get either horrable gas milege or hjorrable gas milege, so what is the point?

<--- drives with windows down and A/C off.

So which is worse? Horrable, Hjorrable, or Horrible?

 

[Atrail]

At highway speeds, I have read that the AC on is more effcient.
In town crusing, windows down is more effcient.

 

[Gunbuster]

does setting the temp dial to less then full cold run the compressor less or just change the air mix?

 

[LongCoolMother]

i saw an article on msn.com before that said one of the ways to get better milage was to use the AC instead of opening the windows. there were probably exceptions, but that was the general rule. their reasoning was that air moving through the car from the windows created too much drag.

 

[JC]

Originally posted by: PsychoAndy


Also, do all A/C compressors have a clutch that frees the compressor from the accessory drive belt when not operating?

-PAB

AFAIK, yes.

And as far as the dual alternator setup, I think the overall drag on the engine would be the same....conservation of energy, you know. Nothing for free Plus you'd have some drag of the second alternator even when not using the AC.

JC

 

[vegetation]

When my AC crapped out a few months ago, I was getting 32-34 mpg when I normally only get around 28 with the AC on all the time. Big difference.

 

[JimmyEatWorld]

Originally posted by: PsychoAndy

Originally posted by: Aquaman
Well.......... you could do an informal test........... drive one tank with AC on and then the next tank with windows down............ just make sure you drive the same style for both tanks of gas Remember.......... the more times you do it the more data points you will have and you will get your answer

Cheers,
Aquaman

The ATOT way of doing things:

We get Brandon's Camry and get it filled up.

Argument as to which gas is best thread ensues.

Cheapest gas wins. Fill up begins.


Argument as to grade commences.

87 octane is decided. One member dies.

Tank full.

Argument as to definiton of full commences. Also, do we shake the hose and get more gas? Do we stop when the handle stops? Do we top off? If so, when? Next dollar, quarter or nickel?

Everyone then gives up. I like research ATOT style!

-PAB

lol

 

[PsychoAndy]

Originally posted by: JC

Originally posted by: PsychoAndy


Also, do all A/C compressors have a clutch that frees the compressor from the accessory drive belt when not operating?

-PAB

AFAIK, yes.

And as far as the dual alternator setup, I think the overall drag on the engine would be the same....conservation of energy, you know. Nothing for free Plus you'd have some drag of the second alternator even when not using the AC.

JC

Ok, one larger alternator then. 200+ amps anyone? Run the A/C compressor off that.

-PAB

 

[Kaervak]

Originally posted by: PsychoAndy

87 octane is decided. One member dies.

LMFAO.

 

[Bobomatic]

even if windows are less efficient, they cool the car down faster. How about windows till the car cools to outside temp, and then ac.

 

[JC]

Originally posted by: PsychoAndy

Originally posted by: JC

Originally posted by: PsychoAndy


Also, do all A/C compressors have a clutch that frees the compressor from the accessory drive belt when not operating?

-PAB

AFAIK, yes.

And as far as the dual alternator setup, I think the overall drag on the engine would be the same....conservation of energy, you know. Nothing for free Plus you'd have some drag of the second alternator even when not using the AC.

JC

Ok, one larger alternator then. 200+ amps anyone? Run the A/C compressor off that.

-PAB

Well again, nothing is free! The overall drag should be the same, it takes (x) amount of energy to run the compressor, regardless of how the energy is delivered.

Can I interest you in a perpetual energy machine?

JC

 

[thomsbrain]

Originally posted by: PsychoAndy

Originally posted by: JC

Originally posted by: PsychoAndy


Also, do all A/C compressors have a clutch that frees the compressor from the accessory drive belt when not operating?

-PAB

AFAIK, yes.

And as far as the dual alternator setup, I think the overall drag on the engine would be the same....conservation of energy, you know. Nothing for free Plus you'd have some drag of the second alternator even when not using the AC.

JC

Ok, one larger alternator then. 200+ amps anyone? Run the A/C compressor off that.

-PAB

You're missing the point. The compressor still takes X number of watts from the engine to run. It doesn't matter where you get it from. In fact, a belt is probably less wasteful because there are less places where energy needs to be converted.

 

[thomsbrain]

Whoa, JC and I said almost exactly the same thing at the same time.

 

[BlueApple]

Originally posted by: PsychoAndy


Argument as to definiton of full commences. Also, do we shake the hose and get more gas? Do we stop when the handle stops? Do we top off? If so, when? Next dollar, quarter or nickel?

OMG you cheap ass

 

[JC]

Originally posted by: thomsbrain
Whoa, JC and I said almost exactly the same thing at the same time.

lol

but you didn't have the perpetual energy quip

JC

 

[PowerMac4Ever]

With AC on most of the time, I get 15 miles per gallon on my 183hp V6. What's up with that?