Windows Down or A/C on? Which uses less fuel?

Doogstar · 09-03-2006, 12:16 AM

Windows down creates more drag on the car, so uses more fuel, yeah?
A/C makes the engine work harder using more fuel, right?

Which uses less fuel?

Does having the A/C fan at a lower setting use less fuel?

**Mechan1k** · 09-03-2006, 12:36 AM

I don't care ... I go for comfort.
There have been numerous tests on this ... it depends on the heat of the day ... speed travelled ... distance travelled ... wind direction ... engine RPM ... Fan speed ... if A/C was running at optimal temps and if it was on MAX or not.

Seriously ... around town ... there wouldn't be much difference at all ... it comes down to what you are comfortable with.

I like to drive with the windows down ... but if it gets a bit too warm ... windows up and A/C on for me.

BlueKoop · 09-03-2006, 12:37 AM

they did that one on Mythbusters .............. AC on is way worse.

Joes_meat · 09-03-2006, 12:41 AM

Apparently windows down uses more fuel once you get about 90ish kmph. Anything less and the extra wind resistance is less than the extra strain from the A/C.

If it's not too hot and I'm traveling around 50 or 60 - I'll leave the A/C off and the windows down.

Mainly for throttle response reasons though.

**Mechan1k** · 09-03-2006, 12:45 AM

When at WOT though A/C shuts off in Falcons/Territories until throttle response is reduced anyway.

AUIII XR8 MAN · 09-03-2006, 12:50 AM

I don't care, if it's hot the a/c is on at what ever speed i'm doing. Really with the new cars these days you don't really use all that much more fuel or loose that much power.

qwigybo · 09-03-2006, 05:05 AM

i like to drive with my window down around other traffic so i can see better (tinted windows) and so i can hear whats going on around me but the a/c is always on

347Stroker · 09-03-2006, 06:51 AM

Always A/C on, never know the difference in power, and I like to be comfortable...

RavenLS1 · 09-03-2006, 07:11 AM

they did this on mythbusters and A/C on uses less fuel.

RavenLS1 · 09-03-2006, 07:13 AM

Quote:

Originally Posted by BlueKoop

they did that one on Mythbusters .............. AC on is way worse.

no mate, it was the other way round and it was only a couple of mills of a litre difference.

LTDHO · 09-03-2006, 07:25 AM

The difference was very small.

So if ya switch ya AC off to save fuel, you are wasting your time!

09-03-2006, 07:28 AM

Quote:

Originally Posted by THE_RAVEN

no mate, it was the other way round and it was only a couple of mills of a litre difference.

Mythbusters should have tryed my XR8 I lose 200 klm off dte when the air con is on when travelling on a hiway ,but comfort is the go so I like to keep mine on even if the windows down a bit

merlin · 09-03-2006, 07:40 AM

My experience is that A/C uses a lot more fuel - dosn't stop me from having it on most of the time though. Although you don't notice the power loss in a car like the Falcon, whenever I borrow my fiances Corolla and you turn the A/C on its like you suddenly pull on the handbrake, very sloooowww.

big_waity · 09-03-2006, 07:57 AM

I honestly think it doesnt matter enough to make someone change their mind. The problem with the mythbuster test was that they had the AC on full blast the whole time, to the point where the dude driving had a massive jacket on. In reality, you would just have it cold enough to be comfy.

My dad did a basic experiment in his AU. on a 300k each way journey, he fueled up, drove there with the windows down, fueled up, drove home with the AC on and then fueled up. It cost him 50 cents more with the windows down. Honestly not enough to matter.

I go for whatever is comfy. If you are that worried about fuel consumption, by an Echo.

Falcon_Phill · 09-03-2006, 08:04 AM

I like having the window down so i can put my arm somewhere, not hanging out like an idiot, just resting it on the sill. Might help if the XF's air conditioning would work too!

merlin · 09-03-2006, 08:17 AM

Quote:

Originally Posted by big_waity

I honestly think it doesnt matter enough to make someone change their mind. The problem with the mythbuster test was that they had the AC on full blast the whole time, to the point where the dude driving had a massive jacket on. In reality, you would just have it cold enough to be comfy.

I dont think there would be any difference between having a/c on high or low, unless cars had inverter type a/c (i.e. variable rate compressors).?

big_waity · 09-03-2006, 08:38 AM

Quote:

Originally Posted by merlin

I dont think there would be any difference between having a/c on high or low, unless cars had inverter type a/c (i.e. variable rate compressors).?

Really? I would have thought that blasting the crap out of the AC would work it harder, thus draining more power. I don't know a whole lot about AC, so I'm just guessing.

Either way, I still dont think it effects fuel economy enough to worry.

Oh, another thing to take into account. One thing I DO know about AC compressors is that they need to be run in order to prevent them from seizing. Not using your AC in winter because it is cold is a bad idea. I often didnt use the AC in my bluebird because I was pretty convinced it drained all 32kw from the bad boy. On a stupidly hot day I put it on full bore and it had seized up from not being used. Since then, I have run mine almost all the time.

I often run the AC with the windows down. I especially love doing it when I'm cruising on a cold night. AC on, full heat, pointed at the feet, it's so neat!

Sorry, couldn't help rhyming there....

:

Des · 09-03-2006, 08:50 AM

Quote:

Originally Posted by Mechan1k

When at WOT though A/C shuts off in Falcons/Territories until throttle response is reduced anyway.

This is obviously why my A/C never feels like it's working!!

Seroiusly though, at anything below about 30-32 degrees I usually have the windows down (front 2 only as the booster seat starts to fly around the cabin with all 4 down), love the sound of a V8 under load. Over these temps, or if the missus is on board, A/C is always on.

BlueKoop · 09-03-2006, 08:52 AM

Quote:

Originally Posted by THE_RAVEN

no mate, it was the other way round and it was only a couple of mills of a litre difference.

did you watch the second part of the episode when they did the real life test not the computer test ...... the car with the windows down did 30 more laps than the car with the ac on...... MYTHBUSTED!!! lol

RavenLS1 · 09-03-2006, 09:52 AM

Quote:

Originally Posted by BlueKoop

did you watch the second part of the episode when they did the real life test not the computer test ...... the car with the windows down did 30 more laps than the car with the ac on...... MYTHBUSTED!!! lol

I must of mist that part.

BlueKoop · 09-03-2006, 09:54 AM

yeah they decided the computer test was not good enough because it based it on the air fuel ratio in ideal circumstances.

Simmo · 09-03-2006, 10:18 AM

yeh i much prefer to put the windows down and listen to my car. plus its only a 6 so AC off is like a turbo boost.

johnydep · 09-03-2006, 10:39 AM

A few years back I read somewhere that the most efficient combination is;
Under 80 km/h - A/C off windows open
Over 80 km/h - A/C on windows closed

But A/C systems have become a lot more efficient over the years, so I doubt that anyone would notice huge differences.

I have tried both in my Territory; when it was new I could see the difference by way of the trip computer, but with 25,000km on the clock the fuel usage is virtually the same with A/C on or off.

MythBusters: Mythbusters Revisited

aquahead2001 · 09-03-2006, 10:55 AM

I did a very rough comparison a few weeks back. I had a BA Falcon hire car and a 3.5 hour drive across south western Victoria. It was a beautiful afternoon with no wind, no cloud and a lovely 26 degrees. On the flat straight roads to Portland I travelled, I had the driver's window down and noted that the average was 8.4 L/100km over about 10kms. I then wound the window up, turned the a/c on and travelled the next 10km. The average was 8.9L/100km.

I did it again the next day on my return to Geelong, when the temperature was well into the 30's, the window down average was 8.6L/100km and the window up + A/C was 9.1L/100km.

Ok, it wasn't the most robust of tests. Another thing I noted was at 100km/h speed I was travelling at, there was hardly any buffeting from having the window down.

Dark Horse · 09-03-2006, 10:58 AM

Uses less with aircon running.

In recycle though the difference is definitely noticeable uses much more go juice.

Fairlane · 09-03-2006, 11:16 AM

bahh you sissies, real men but the heater and the windows up when they want to go fast and save fuel.

But jokes aside, i think factors such as having an extra passenger in the car or running with a low tyre pressure would have a similiar influence on fuel economy as having the aircon on or off.

henry 351 · 09-03-2006, 01:05 PM

Who cares? If you've got airconditioning use it when you want. It's also great for defrosting in winter or removing steamed up windows, just use it with the heater on.

I was out Saturday in the old 400 cube Galaxie, 34 degrees, doing 70 mph with ice cold airconditioning, stuff putting a window down for a gnats tear worth of juice...

Steffo · 09-03-2006, 01:15 PM

Well, my car has no gas in the a/c so that only blows hot, so I rely on the windows.

I won't be keeping it long enough to care as the heater works and colder times are on their way, but let me tell you, I'd 100% rather have a/c then save a bit of fuel and have the windows open.

Dauphin · 09-03-2006, 01:38 PM

Maybe if you've got a clean run at 100km/h for a while then having the air con might be fine but if you're stuck in heavy traffic and you have it on, it should be a big negative difference, right? But it's probably better than having the heat from the engine bay next to you coming in open windows, including the smells!

Ben083GC · 09-03-2006, 03:51 PM

Quote:

Originally Posted by Dauphin

Maybe if you've got a clean run at 100km/h for a while then having the air con might be fine but if you're stuck in heavy traffic and you have it on, it should be a big negative difference, right? But it's probably better than having the heat from the engine bay next to you coming in open windows, including the smells!

True, in heavy traffic the heat from the car when the windows are down at times can be pretty hot, so il tend to go AC. When not in heavy traffic, the windows down for sure.