Use the A/C or the Windows...not both

When you have your ac running youre basically making a parisitic effect on your cars power. And when you roll you windows down its like opening up a sail on top of your car. They both consume your cars precious power and gas so next time use one or the other.

yeah i was watching myth busters one time and they did a test at a constant 50 mph on a track and actually got better mileage with the ac on and windows up than they did with the ac off and windows open. having both ac on and windows open really doesnt make any sense at all unless maybe you are smoking and you forget to turn off the ac lol...

i suppose you would get better mileage with windows down and ac off when driving in city traffic due to stopped periods of time and also lower speeds that make less of an effect with windows making a less streamlined shape when down

Also its economically more efficient to keep your truck tailgate up instead of down. Aerodynamics shows that the air makes a small pocket in the bed and the air flows smoother if the tailgate is up. (Also from mythbusters lol)

yeah i was watching myth busters one time and they did a test at a constant 50 mph on a track and actually got better mileage with the ac on and windows up than they did with the ac off and windows open. having both ac on and windows open really doesnt make any sense at all unless maybe you are smoking and you forget to turn off the ac lol...

i suppose you would get better mileage with windows down and ac off when driving in city traffic due to stopped periods of time and also lower speeds that make less of an effect with windows making a less streamlined shape when down


Actually they found, using electronics, that ac was supposed to give them better gas mileage than the engine without ac. then they took 2 suv's one using ac, and one with the windows down and the suv with the windows down went much much longer. they only used one gallon of gas.

The AC vs windows debate is an old one. If you're constantly moving at high speed, then the AC on with windows up gives the better mileage, as wind resistance grows with speed while the AC resistance stays pretty constant.

However in stop and go or at lower speeds, the situation is reversed, as the constant drain of the AC is greater than the variable wind resistance. Each vehicle has a different speed for AC vs. wind resistance, but figure that most vehicles traveling less than about 45-50, (where wind resistance builds rapidly) get better mileage with the windows down and AC off.

i think the test that myth busters did was at either 50 or 55mph and they found that windows down gave he best mileage.

Yes, the windows down gave the better mileage. The overall effect of having the windows down on total drag coefficient is very small. Windows down gives better mileage than A/C in almost every case. Certain exceptions exist I'm sure for certain vehicle shapes and particularly high-draw A/C units, but in general windows down is always the mileage saver.

Yeah, windows down is preferred if you have a tailgate window to put down too so the air can flow through. I've seen a dozen of these shows since the 70s and they seem to rotate which is better so I go with the common sense approach. If I'm doing 70, the windows are up because wind into the car creates drag when it hits the back window. If I'm doing 40, windows down because there isn't enough wind to cause drag. If you've ever ridden a motorcycle at 70 mph, you know how much drag wind hitting you can be (why bike racers lay down on the gas tank). I figure an A/C unit doesn't create as much.

also though, you have to consider how much are you rolling down the windows?

My A/C is broken. so on the highway if I'm doing 80, I have to open the windows to stay cool. But I simply pop my window open a couple inches, then I open the window behind it a couple inches more. There are ways to roll the windows down which create a lot of drag, and there are better ways to roll them down which create far less drag. You just have to experiment. I do 80-90 on the highway with windows down, and it's not even windy in my car, but it still allows the hot air to escape.

Ok it was mentioned that bigger vehicles with bigger engines with SUV's get better gas mileage with the A/C on. I know they have more engine power to spare compared to smaller vehicles. My Neon only has a 2.0L engine in it. Wouldn't that extra it takes to keep that air conditioner working not be worth it with a smaller engine because it would have to work way harder? BTW I really don't have a choice unless I get the air conditioner fixed :D

I'd think a Neon would have pretty low wind resistance compared to a large SUV, so the savings for having the AC off would be larger.

large suv's don't always have high wind resistance. the new cadillac escallade (sp) has the same coefficient of wind resistance as a corvette.

We only have one vehicle that has A/C and I don't use it. For one, I don't trust A/C systems - we had a neighbor that died of legionaires disease and I'm continuously lysoling our home A/C.

With that said, my A/C system really takes alot out of the Taurus - the torque converter is constantly unlocking and locking beucase it takes so much. When I turn the A/C on, I have to press the pedal alot farther. Plus, I like the feel of nice warm air blowing over me anyway.

But who realy has the windows all the way down.

I have two windows down 1/4 and put the fan blowing on my feet for circulation.

"the new cadillac escallade (sp) has the same coefficient of wind resistance as a corvette."

Yes, but the Escalade has more frontal area so it has a greater total drag.

"the new cadillac escallade (sp) has the same coefficient of wind resistance as a corvette."

Yes, but the Escalade has more frontal area so it has a greater total drag.

huh?

The drag coefficient Cd only measures how efficient the body shape is at moving thru the air, it has to be multiplied by the frontal area of the vehicle to get the true drag, carmakers will usually only quote the drag coefficient but not the frontal area. As an example, I remember that the original Dodge Caravans had a Cd of 0.43, so did the Dodge Omni. But it's obvious that the smaller Omni(looks like an older VW Rabbit/Golf) had a smaller front area presented to the air and therefore less drag.

Typesix, (Post #17), smart post.

Also, adding flares, spoilers, fins, and wider tires all add to frontal area, and increases drag and weight.

To all the posters who understand the difference between tests with ac vs. 100% windows down, and the real world with windows partially down...
...way to go people.