Fact #568: April 27, 2009
For Modern Cars, Replacing an Air Filter Will Improve Performance but Not Fuel Economy
A February 2009 study conducted by Oak Ridge National Laboratory found that for modern computer-controlled, fuel-injected engines, changing a clogged air filter has no measurable affect on fuel economy but does affect ultimate performance. Average acceleration times for the vehicles in the study improved by 6 to 11 percent when running on a clean filter. The fuel economy of carbureted engines, which went out of production in the early 1980s, was impacted by a dirty air filter. The study found that typical fuel economy gains for replacing the air filter on the carbureted vehicle were in the range of 2 to 6 percent.
WOT – Wide-open throttle
MPH – Miles per hour
A clogged filter was defined by a level of airflow restriction that was sufficient to activate a common indicator light inside the vehicle showing the air filter needs changed. On all vehicles, the level of restriction was on the order of 6.0 to 7.0 kilopascals (kPa – pressure unit).
|Test Vehicle||New Air Filter||Clogged Air Filter||Seconds||Percent|
|2003 Toyota Camry||17.24||18.51||1.26||7%|
|2007 Buick Lucerne||13.77||15.45||1.68||11%|
|2006 Dodge Charger||10.23||10.84||0.61||6%|
* Wide-open throttle.