We Test the Tips

Test #4 A/C On, Windows Up vs. A/C Off, Windows Down

This has got to take you back to the days with the family on vacation. Dad says, "Turn the A/C off! It wastes gas!" And Mom says, "We can't roll the windows down or everyone on the highway will think we can't afford A/C." And you're in the back roasting, hoping someone will win the argument so you can cool off.

Well, family psychology aside, if dads are still saying this, they aren't necessarily right. While the A/C compressor does pull power from the engine wasting some gas, the effect appears to be fairly minimal in modern cars. And putting the windows down tends to increase drag on most cars, canceling out any measurable gain from turning the A/C off. But this one depends on the model you're driving. When we opened the sunroof in our SUV, the mileage did decrease even with the A/C off. Still, in our experience, it's not worth the argument because you won't save a lot of gas either way. So just do what's comfortable.

Method: We drove the full 55 mile-loop in two cars at equal speeds both times — 65 mph. The first loop we drove with the A/C on and the windows up. The second loop we drove with the A/C off and windows down. In the second test we drove 20-mile loops. This was far enough to see our gas mileage level off and remain steady on the computer trip meter.