Common A/C and Fuel Efficiency Myths Debunked

 
Two A/C myths always seem to crop up as the temperature climbs higher and long road trips become commonplace.

Myth #1: 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.

Myth #2: 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.

Car_air conditioner

Uncovering the truth

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 3% (versus keeping it off). In another test they drove at 65 mph, but this time with the windows down. They 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% 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 the bottom line:

  • Using a vehicle’s air conditioner may result in a small decrease in fuel mileage. As the driver, you get to choose what to do with that knowledge. Maybe 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).

How to really improve fuel economy

If you want to improve gas mileage, try some of these fuel-saving strategies instead:

  • Slow down and avoid aggressive driving, such as hard accelerations and hard braking. Driving normally will increase fuel mileage by as much as 33% at highway speeds.
  • 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 3-4% improvement in fuel mileage.
  • Consolidate trips: do all your errands in one run

What do you think? Do you prefer to sweat if it saves you a few pennies, or is it a small price to pay for personal comfort? Leave us a comment.

Last updated June 5, 2017

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