Recently, I wrote an article on the debate; do you get better mileage with AC on and windows up or AC off and windows down? A comment in the article said a Mythbusters episode found you could get better mileage with AC off and windows down. The way Mythbusters tackled the myth in that episode was just horrible. The myth was revisited in another episode, which I ordered and will review soon. So, what did they do?

They got an SUV and attached a sensor that estimates mileage by measuring air flow to the engine. They did 15 laps around a track, with a constant speed of 45 MPH, measuring mileage as they went. They did 5 laps with the AC off and windows down. 5 laps with AC off and windows up. 5 laps with the AC on and windows up. No laps for AC on and windows down. Here are the results.
  1. AC off, windows up = 11.7 MPG
  2. AC off, windows down = 11.3 MPG
  3. AC on, windows up = 11.7 MPG
So, according to these tests, AC use does not impact mileage. Windows down hurts mileage about 5 percent. The better option is turn on your AC. Rolling down your window makes little difference at all. Apparently unsatisfied, they tried a totally new test, measuring mileage differently and even changed the variable of speed. This is important for the revisit which showed speed was very important. How they did second test is after the jump.

They get two SUVs and emptied the gas tanks. Then filled both tanks with exactly 5 gallons of gas. They both drive around the track, same loads, this time at 55 MPH. One SUV has AC off and windows down, while the other has AC on and windows up. The AC on and windows up SUV stopped first. The AC off and windows down SUV went a 15 percent greater distance.

So, if you trust this test, AC burns 15 percent more gas. Windows down is the way to go. They end by saying they did not really trust the first test because it was just an estimate. The second test was full proof and show the best option for saving fuel and keeping cool was windows down and AC off. Where to start with the mistakes? First, you don't change your testing methods because you don't like the results.

It's really the first rule of the scientific method. You have to attack the method of estimating mileage with air flow. You can't just say, it did not do what I wanted, so it's useless. What's the point of an experiment if you can do that? Didn't they look into if air flow could measure mileage before hand? They should do experiments or research on the how sensitive air flow measurement is in estimating mileage changes.

Changing the speed to 55 MPH in the second test is just inexplicable. They had enough problems going to a different way of measuring mileage and not doing enough experiments. In the middle of all of that, why throw in another variable? They really needed to do a lot more trials and be a lot more careful. I really don't have much hope for their methods in the revisit. These are really basic mistakes.

[Source: Mythbusters]

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