Fact #568: April 27, 2009 For Modern Cars, Replacing an Air Filter Will Improve Performance but Not Fuel Economy

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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.

Performance Benefit to Changing a Clogged Air Filter on a Modern Vehicle
Graph showing the performance benefits to changing a clogged air filter on modern vehicles such as the Toyota Camry, Buick Lucerne, and Dodge Charger. For more detailed information, see the table below.

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).

Supporting Information

Acceleration times 20 to 80 MPH at WOT* (Seconds)
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.
Source: Kevin Norman, Shean Huff and Brian West. Effect of Intake Air Filter Condition on Vehicle Fuel Economy, Oak Ridge National Laboratory. Report: ORNL/TM-2009/021. February 2009 (PDF 1.0 MB). Download Adobe Reader.

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