I know AC consumes more gas with it on, but how does that compare to having open windows and extra drag?

Most of my driving during the week isn't highway, but mostly local roads where it's not much stop and go. I drive about 45 miles/day just to and from work. Normally I have my windows and sunroof open, cause I like the wind blowing.

But this week, it was just too hot. So I used my AC the entire time (morning and night). I didn't drive any different then I normally do, and I didn't change anything in my car (not even air pressure). But somehow this week, I got much better gas milage.

Normally the way I drive I go about 300 miles and it takes about 14 gallons to refill my tank (about 21.5 MPG). This week at 300 miles it only took me 12.5 gallons to refill my tank (24 MPG). I noticed I was getting better gas milage, but didn't realize how much.

I alway go to the same gas station and always allow the pump to fill til it shuts off, so I know my numbers are pretty accurate. I knew that over 45 MPH, AC is more efficent then windows open. I guess I never realized how much better.
Has anyone else had similar experiences?

 

hmmm...interesting. Is it possible that there was another variable involved. Maybe a different driving style or something? You are right on the A/C being more economical at higher speeds - but even 45MPH seems low. There isn't much wind resistance to at that speed. Maybe you were driving a little more conservatively knowing the A/C was or something perhaps?

As for my gas mileage - driving without the A/C in the summer isn't an option in the TX heat. And most of my trips are less than 10 minutes or so where the engine is still running in warm-up mode. I still average about 20-21 MPG. The best I ever got was 28.5 MPG where it was mostly Cruise set at 80 MPH.

 

i think your fuel economy going fairly fast will be better with AC on rather than having all the windows down

 

I believe the general rule is during normal driving it is more efficient to open the windows but at highway speeds its better to use the air conditioning cause of the drag.

 

I thought I read the cutoff was 30mph... below use open windows, above use AC.... and it makes sense with what you observed.

 

If there are any other motorcyclists here, you'd know that at 45 MPH wind is pretty intenst. Especially if you've ever driven without a helmet on. CT drivers???

Keep this in mind. Winds at 50+ MPH during storms blow over trees!

 

That's why right there. It takes much less power, which kmeans gas, to run the compressor at a constant speed than it will to accelerate over and over again with the extra drag the compressor produces. Of course the drag thing like others mentioned also comes into play, but is more a factor at higher speeds, but your steady state driving is why you got better mileage in this case, even though it was relatively low speed.

 

My friend would never turn the AC cause he thought he'd get much worse gas mileage, plus he's a cheap Bastard.

I tried telling him, that if it's not much stop and go and you're going over 45 mph, it's better to use the AC. He didn't believe me. Guess I now have something to back up my statements.

 

guys... it even says you get better MPG with A/C on at highways speeds in your owner's manual.

 

What's highway speeds? My drive to and from work is usually 35-45, but it's pretty steady and not stop-and-go.

 

I honestly don't like my car with A/C on because of lack of power. I hardly ever use it when going under 40. But if it gets really hot than forget it. Below 45mph open windows after use A/C that's my general rule!

 

If it's not too hot and I'm travelling at highway speeds, I crack the sunroof and open the rear passenger side window to the max. Lets in a nice cooling breeze but I don't think it could ruin fuel economy as much as having even one of the front windows down.

 

does running the a/c make ur car lose that much power?

 

Try this: accerate hard on the highway and turn on the AC while still accerating. You should feel the difference. It's not a huge change but it is there.