Well I guess they like breathing in dirty air then....

[AmbrosiaWriter]

It seems like a lot of people in this thread have not watched Mythbusters!

They did this VERY experiment. They filled their vehicles (both same make, model, and year) up to full, then drove on and on. One had windows up, AC on, the other windows down, no AC.

The windows down, no AC car won by a LONG shot in terms of gas efficiency.

While it wasn't a SUPER, SCIENTIFIC TAKE EVERYTHING INTO ACCOUNT test; it's good enough for me in terms of just daily general knowledge.

[greek_jester]

Also, while I'm too lazy to look up a link to the episode, Mythbusters did a test of this with 2 SUVs of the same type with similar amounts of fuel. The one with windows down drove approx. 50 miles further than the one with AC, if I remember correctly.

IIRC from other studies, if you're urban driving (20-40mph) it's better to drop the windows as the drag isn't enough to really affect mileage much, while over 40mph it's better to use aircon on low, as the drag effect is higher than aircon.

Weirdly I use the aircon more often in winter than in summer; it clears the windscreen much faster while I'm scraping the snow and ice off if I put the aircon on, rather than just heat alone.

[Ophbalance]

The MythBusters found that under 45 MPH it's more economical to keep the windows down over using A/C. Keep in mind they were using vehicles that display a goodly amount of air.

And for the record, there is no hyphen in Hypermiler.

Personally I've found that newer vehicles tend to have much less engine drag running moderate A/C vs what was available 10 years ago. My Civic could barely hold highway speeds with A/C on. The Elantra would physically chug as well. The Sedona/Prius/Escape? I cannot even tell when the compressor kicks in.

Essentially "all things in moderation". If I set the A/C at an automatic setting of around 79F, which seems high but it still blows ice cold when it's above 80F outside, I get negligent MPG hits. Now lets take that same trip with my spouse. The blower fan gets set to Gale Force Powah!!(TM) and the temp to 75F. It easily brings my MPG hit down by 5 or more MPG.

You also have to take into account the speeds you're traveling. Anything above 65 MPH for most vehicles and you can see the MPG start dropping like a stone. I know someone mentioned earlier Kw for highway load. The Prius runs between 12-16 Kw on level ground at 65 MPH. It takes surprisingly little Kw to keep a car moving down the road at a given speed... it's the acceleration that kills you.

[sld72382]

Well down here in the sunshine state I only keep the driver's side window open for a few minutes to get the hot air out of the car, put the A/C on full blast then close it.

Sorry but I don't care if I lose a few mpg I'm not stifling in a hot car just to save a buck or two when I go to the gas pump. And no, I'm not leaving my windows down because down here even when it's windy it's like a blowdryer.

[Peppergirl]

Sorry but I don't care if I lose a few mpg I'm not stifling in a hot car just to save a buck or two when I go to the gas pump. And no, I'm not leaving my windows down because down here even when it's windy it's like a blowdryer.

This. I just moved down to the sunshine state, and I have to watch my money like everyone else. However, there's simply NO way I'm driving around with (like you describe) my car feeling like a blowdryer with the windows open. And that's exactly what it feels like...till October, at least.

I'll gladly cut corners somewhere else so I can have my AC at least moderately running in the car.

[Catwoman2965]

This. I just moved down to the sunshine state, and I have to watch my money like everyone else. However, there's simply NO way I'm driving around with (like you describe) my car feeling like a blowdryer with the windows open. And that's exactly what it feels like...till October, at least.

I'll gladly cut corners somewhere else so I can have my AC at least moderately running in the car.

I live in NJ, but detest the heat. I do notice A slight drop in mpg (based simply on how long I can go before needing gas) when I run the a/c vs. not. But i hate the noise with my windows open, and I'd rather be cool, if not cold. But it really makes very little difference to me. I bought my new (to me) car in May, and until now, haven't really driven without the a/c since then!

[Caractacus_Potts]

In my experience, this is not the case at all. The 'extra' drag from opening my windowas had no noticeable effect on my overall gas mileage.

Running the AC knocks an immediate 5 mpg off the fuel efficiency.

Running the heat knocks an immediate 3 mpg off the fuel efficiency.

That's been the case with my last 5 vehicles, which accounts for every car I've owned for the last 20 years.

Well...the heater uses excess heat from the engine and has no effect on fuel economy so based on your figures you have a +/- 3 mpg margin of error which means you may very well be getting the same mileage with windows down as you do with A/C (or slightly better, or slightly worse).

You and some others have pointed out that MythBusters has proven that when driving a large vehicle at relatively low speeds windows down is more fuel efficient than A/C. Oak Ridge National Laboratories did more comprehensive testing which showed that there is a cross-over point at higher speeds where using the A/C is more fuel efficient, at least for smaller vehicles.

I guess if you want to micro-manage your fuel economy and you own something smaller than an SUV then you should use the A/C when driving at highway speeds and switch over to open windows at anything less than highway speed. If you own an SUV or larger just stick with open windows, you'd get one hell of a ticket if you were driving fast enough in an SUV for the A/C to be more efficient.

[cashierbex]

This. I just moved down to the sunshine state, and I have to watch my money like everyone else. However, there's simply NO way I'm driving around with (like you describe) my car feeling like a blowdryer with the windows open. And that's exactly what it feels like...till October, at least.

I'll gladly cut corners somewhere else so I can have my AC at least moderately running in the car.

Florida heat sucks. I am glad its cooling off in the mornings. I don't have my AC on then. I cannot wait for it to be winter. 30 degree weather would be nice where I live for a month. I miss snuggling up in my sweaters.

[Peppergirl]

Florida heat sucks. I am glad its cooling off in the mornings. I don't have my AC on then. I cannot wait for it to be winter. 30 degree weather would be nice where I live for a month. I miss snuggling up in my sweaters.

Me too. Im in north-central, which is usually super hot in the summer but cold-ish in the winter.

As for sweaters...I can relate. Im a HUGE hoodie fan. I keep eyeballing my packing box (just moved here in June) marked "myname Winter stuff". Eagerly awaiting when I can open it, like a damned kid in a candy store.

But yeah, I'll gladly trade in MPG to NOT have it feeling like a hairdryer when the windows are open.

[Fire_on_High]

I'm in GA....tiny, old car so I skip both heat and ac. It's a learned appreciation...

[protege]

Sadly, the number of quick lube places that try to sell you a load of stuff you don't need is pretty damn large.

Unfortunately, this is very true. I've seen all sorts of things at shops over the years--chemicals that supposedly clean fuel injectors, increase mileage, or other "benefits" usually at a hefty cost. Other than fuel injector cleaners, none of these things do what they're claimed to do.

Anyway, I wouldn't bother paying a shop to change my car's cabin air filter. Why pay an arm and a leg (labor rate locally is about $95 per hour ) when I could get the filter and do it myself? Plus, I don't use the A/C much anyway. Most of the time, I'm sitting in traffic, and have the windows down. On the highway though, the A/C comes on. I don't know about you, but I don't like the roar at 70mph

[wolfie]

Well...the heater uses excess heat from the engine and has no effect on fuel economy so based on your figures you have a +/- 3 mpg margin of error which means you may very well be getting the same mileage with windows down as you do with A/C (or slightly better, or slightly worse).

On older VWs, and on the Chevy Corvair, the heater is a separate fuel-burning device rather than using waste heat from the engine. Naturally, fuel economy takes a hit when you use the heater on those vehicles.

[protege]

On older VWs, and on the Chevy Corvair, the heater is a separate fuel-burning device rather than using waste heat from the engine.

They're also a bit cold on the move. No engine up front means that they take awhile to get warm in the cabin. When my parents had a VW 412 station wagon, we would wrap ourselves up in blankets