The contrarian in me loves it when conventional wisdom is proven to be not so wise. For decades, even before the first oil crisis of the 1970s, motorists have been told that making sure that your air filter is clean is one of the ways that you can improve  your fuel economy. It’s intuitive to think that a clogged air filter will affect the way an engine “breathes”, how efficiently it can get gases in and out of the combustion chamber and how that might decrease fuel economy. That may have made sense decades ago, however it turns out that two different studies, one on gasoline engines and the other on diesels, performed by a team at the Oak Ridge National Laboratory, show that the fuel economy of modern, digitally controlled fuel injected engines isn’t significantly affected by the state of their air cleaners’ cleanliness. What made sense in the era or carburetors may no longer be applicable today. Apparently the engines’ ECUs working to keep emissions in spec are capable of leaning out the fuel mixture to account for a dirty air filter restricting airflow into the engine, resulting in insignificant drops in fuel economy. Though dirty air filters didn’t materially affect fuel economy in the modern cars, they did experience a decrease in acceleration performance so it’s still a good idea to replace a dirty air filter.

Abstracts of the studies after the jump. (Read More…)