Your A/C: Car Myths Debunked!

Car_air conditioner

Myths – they’re everywhere, and particularly online. Plenty of those myths focus on cars, like the one about it being better to fill your tank in the morning because the fuel is colder and denser (it isn’t) and you’ll get more for your money (you won’t.) Or there’s the one about increasing your pickup truck’s fuel mileage by driving with the tailgate down to reduce wind resistant (false, as pickups are designed to be aerodynamic with the tailgate up).

I’d like to investigate two myths that always seem to crop up when summer rolls around, the temperature climbs higher, and the long road trip becomes commonplace. It’s this myth: a vehicle’s air conditioner causes the engine to work harder. Therefore, electing not to use the air conditioner and instead rolling down the windows when driving will significantly increase fuel mileage. And in a similar vein there’s this myth – driving with your windows down will significantly decrease your fuel mileage because of the increased aerodynamic drag the open windows create.

One myth probably has some truth to it and one is most likely false. Here’s why.

In a test conducted by Consumer Reports, they drove a Honda Accord at 65 mph and found that using the air conditioner reduced fuel mileage by three percent. In another test they drove at 65 mph but this time with the windows down and found no measurable effect on fuel mileage. In a similar test performed by Edmunds using a Toyota Tundra, they saw a decrease in fuel mileage of almost 10 percent when using the air conditioner as opposed to driving with the windows down and the air conditioner off.

There are many similar tests and results online, but here’s what I think is the bottom line. It’s a conclusion similar to that reached by many of the testers:

  • Using a vehicle’s air conditioner may result in a small decrease in fuel mileage. However, that decrease is negligible compared to the discomfort of not having air conditioning on a hot summer day.
  • Driving with a vehicle’s windows rolled down doesn’t produce any measurable impact on fuel mileage as a result of aerodynamic drag (but your dog will love it if he’s along for the ride!)

If you really want to improve gas mileage during an epic road trip this summer, pay attention to these fuel-saving strategies instead:

  • Slow down and avoid aggressive driving, such as hard accelerations and hard braking and increase fuel mileage by as much as 33 percent at highway speeds, according to the official U.S. government source for fuel economy.
  • Remove excess weight from the vehicle and avoid hauling bulky items on the roof because it increases aerodynamic drag.
  • Keep your engine in tune and tires inflated to the recommended air pressure for a three to four percent improvement in fuel mileage.
  • Consolidate trips or share rides with someone else.
  • Drive a fuel-efficient vehicle.
  • Get more fuel-saving tips.

It’s not a bad idea to brush up on your  A/C-testing skills either because cold A/C makes for a comfortable car temperature. If you think your air conditioning might be malfunctioning, measure the temperature accurately by sticking this A/C thermometer in the vent with the A/C turned on. It might be working fine or you might need a simple fix. Either way, you’ll have an accurate temperature reading to help you decide.

For me, even on a hot summer day, if I’m driving on back country roads or on the highway, I prefer having the windows down and the A/C off. There’s just something about fresh air that I love. But driving around town, having the A/C on wins hands down every time. What do you think?

Editor’s note: Visit Advance Auto Parts for helpful advice and even better values. Buy online, pick up in store—in 30 minutes.