It may be overlooked, but the appearance of your car can actually effect it’s miles per gallon. When it comes to aerodynamics, a waxed or clean car will allow air to move freely across the surface (less resistance). Unlike a clean surface, a dirty car limits the amount of airflow, causing increased friction and less MPG. Unfortunately, we didn’t coin this finding, but the experts at MythBusters did it for us.
In their study, on Episode 127, they tested the same car twice (once dirty, once clean) to determine if the myth was plausible. After a series of tests, the clean car averaged 2 MPG more than the dirty car.
“Adam and Jamie covered a car in dirt and mud and drove it down a track at highway speeds to measure its fuel efficiency, and repeated the test after the car was cleaned. They discovered that the average gas mileage for the dirty car was 24 miles per gallon while the clean car performed better at 26 miles per gallon.”
As you can see, even the experts know it… a clean car means more than a great shine.