Gas Savings Tips That Don't Actually Work

[Trevloc]

from mythbusters:

Running a car with air conditioning on is more fuel efficient than running with the windows down.
partly confirmed*

Tests were performed under varying conditions (55 mph versus 45 mph). The 55 mph test used a computer to estimate fuel efficiency based on air intake, not actual fuel consumption, and showed A/C was more efficient. The 45 mph test consisted of running the tank until it was empty, and showed open windows were more efficient.

*Because the original tests were inconclusive, this "urban puzzle" was revisited in episode 38: It is more fuel efficient to use air conditioning when the car is traveling approximately 50mph or more. Otherwise, windows are more fuel efficient.

 

[Ross]

from mythbusters:

Running a car with air conditioning on is more fuel efficient than running with the windows down.
partly confirmed*

Tests were performed under varying conditions (55 mph versus 45 mph). The 55 mph test used a computer to estimate fuel efficiency based on air intake, not actual fuel consumption, and showed A/C was more efficient. The 45 mph test consisted of running the tank until it was empty, and showed open windows were more efficient.

*Because the original tests were inconclusive, this "urban puzzle" was revisited in episode 38: It is more fuel efficient to use air conditioning when the car is traveling approximately 50mph or more. Otherwise, windows are more fuel efficient.

Mythbuster is entertaining but there way of testing isn't always that good.

This will depend on the design of the car. To accurately test you can only have one variable. In this case window up or window down. The car would have to be the same, the temperature, the same humidity, the same gasoline, etc. If you have more than one variable you don't have a good test. You also have to conuct mulitpe tests. You would have to test each type of car. A Porsche 911 vs a Toyota 4Runner could show different results.

 

[Trevloc]

Mythbuster is entertaining but there way of testing isn't always that good.

This will depend on the design of the car. To accurately test you can only have one variable. In this case window up or window down. The car would have to be the same, the temperature, the same humidity, the same gasoline, etc. If you have more than one variable you don't have a good test. You would have to test each type of car. A Porsche 911 vs a Toyota 4Runner could show different results.

on the espisode, they had the same variable. they had two cars of the exact type. if i recall right it was a jeep cherokee or something of that nature. and they put the exact same amount of gas in them, like 16 gallons ish?. and they went to a race track, one had the a/c at full blast the whole time, and one had windows down the whole time and they drove in circles around the track til they ran out of gas. ill see if i can find a link to the video.

 

[Ross]

on the espisode, they had the same variable. they had two cars of the exact type. if i recall right it was a jeep cherokee or something of that nature. and they put the exact same amount of gas in them, like 16 gallons ish?. and they went to a race track, one had the a/c at full blast the whole time, and one had windows down the whole time and they drove in circles around the track til they ran out of gas. ill see if i can find a link to the video.

I deal in testing so from my perspective that would not be legit. It would have to be the same vehicle. It would have to be proven to operate consistently under controlled conditions. The gas would have to deal with the same manner. Nothing that had "ish" involved would pass. It would have to be repeated multiple time and yield the same results.

Not every car performs exactly the same, even if it the same model. One could have issues with its fuel injector or fuel pump or whatever little things that can affect gas mileage.

I would agree that with the windows up and down you will create more or less drag. The amount of resistance at difference speeds would vary and at some point in time could have a greater effect on gas mileage. But this will never be a constant esp. between different cars or situations.

 

[Trevloc]

I deal in testing so from my perspective that would not be legit. It would have to be the same vehicle. It would have to be proven to operate consistently under controlled conditions. The gas would have to deal with the same manner. Nothing that had "ish" involved would pass. It would have to be repeated multiple time and yield the same results.

Not every car performs exactly the same, even if it the same model. One could have issues with its fuel injector or fuel pump or whatever little things that can affect gas mileage.

I would agree that with the windows up and down you will create more or less drag. The amount of resistance at difference speeds would vary and at some point in time could have a greater effect on gas mileage. But this will never be a constant esp. between different cars or situations.

i agree that they should use the exact same vehicle twice. i think they used 2 to save time.

 

[Quentin]

I think the AC or windows heavily depends on vehicle design and passenger tolerance. On my last car, a MKV VW GTI, I could just slightly crack the passenger side windows (front and back), and air would move through the cabin very, very well. Up into the 80s, I was very comfortable driving like this. I can't imagine the aero drag was too badly affected by this. That said, I didn't have the tolerance to handle the noise at interstate speeds, so I used the AC at that point.

 

[Awz]

Air filters need to be replaced. Air flow and fuel consumption maybe monitored closely but that doesn't mean the engine isn't working harder to GET the air into the engine. Even on vehicles with RAM-AIR (the idea being your speed 'RAMS' air into the engine) the engine is sucking the air in. The dirtier your filter the harder this is to do. All things follow the path of least resistance, if it's hard to get air from the filter, it'll find a whole somewhere (I've seen this when I worked for Saturn) then you get unmetered air, and lots of other problems. I work for Subaru now, and see very dirty air filters almost everyday. Some of these you can SET on the table, when you pick it up there's a pill of dirt under it. I can't believe replacing that wouldn't improve fuel economy throughout the driving range. There's a reason people use cold-air intakes, and cone filters.