Can a Clean Car Get Better Gas Mileage Than a Dirty One?

How often do your wash your car? Once a month? Maybe twice a year? Whatever the answer is, we bet that you would likely wash it more often if you knew that doing so would result in better fuel economy. But is that even possible?

Does a clean car equate to better fuel economy?

Two men wash a car.
Two men wash a car. | Getty Images

RELATED: Common Car Washing Practices That Will Ruin Your Car

Yes, it does! We know, it’s a shocking revelation. But the folks over at MythBusters put this experiment to the test in one of their shows once upon a time. Their original hypothesis was that the dirt on a car would cause a “golf ball-like effect” that would improve its aerodynamics and thus improve its fuel efficiency. To conduct the test, host Jamie and Adam utilized an old Ford Taurus and made multiple runs with it to test its overall fuel efficiency.

To test it when it was dirty, they caked the car in mud and ran it a few times. Afterward, they cleaned the car and ran the tests again. According to the Clean Tools blog, the duo ran multiple tests to ensure the accuracy of the experiment. The results concluded that the car was more efficient by 2 mpg when it was clean as opposed to when it was dirty. More specifically, the car achieved up to 24 mpg when it was dirty and 26 mpg when it was clean.

Why does a clean car achieve better fuel efficiency?

While it might seem weird that a clean car can achieve better fuel economy, it’s not. In fact, it really comes down to aerodynamics. The protruding dirt and debris on your car create a rougher surface for the outside air to flow around. Due to this buildup, your car will have more resistance when traveling down the road, which becomes greater the faster you drive it.

However, if you clean the car – especially if you wax it – you will create a smoother surface for the outside air to flow around the car, which results in better aerodynamics. After all, when automakers conduct wind tunnel testing on their cars, they’re usually spot-less. This ultimately means that if you want to marginally improve your car’s gas mileage, just remember to give it a good wash. Hopefully, more than twice a year.

Here are some more tips for better fuel economy

A car is covered with mud and dirt.
A car is covered with mud and dirt. | Robert Alexander/Getty Images

While washing your car is an easy way to improve its fuel economy, there are plenty of other ways to squeeze out more miles per gallon. Here are a few methods provided by AAA:

  • Drive conservatively: Avoid “jack rabbit starts” or quick acceleration from a stop in addition to hard braking. Doing so can increase your car’s fuel economy by 10 to 40% in stop-and-go traffic.
  • Use cruise control: Using your car’s cruise control will allow it maintain a steady speed on the highway, which can equate to more miles per gallon.
  • Avoid excessive engine idling: When you let your car’s engine sit idling, especially when it’s cold, it’s getting 0 mpg. In that case, if you can, shut the car off if you’re going to let it idle for more than a minute.
  • Drive at the speed limit: We know, it’s hard to stick to the speed limit on any road, but doing so can help with your car’s gas mileage since you’re driving slower.

RELATED: When Should You Use a Waterless Car Wash?