Changing Your Air Filter Improves Your MPG – Debunked!

If you are changing your air filter before the manufactures recommended service interval than you are just throwing money away.

A study on air filters done by Oak Ridge National Laboratory for the U.S. Department of Energy concluded that a dirty air filter has NO effect on MPG for any vehicle with an engine control system including fuel injection  and very little on older carbureted vehicles.

How can that be as it is clear a dirty motor will not run as efficiently right? Well, in reality the air filter is keeping dirt out of your motor and the more dust or dirt on it makes it more difficult for anything to pass through not easier so your engine isn’t dirty – the filter is. Most vehicles built in the last 20 years incorporate what is called a closed loop fuel control that effectively controls the air needed through a throttle control that easily compensates for any dirt on the filter.

According to the Society of Automotive Engineers the standard recommended service life for an air filter in light- and medium-duty applications, is about 30,000 miles. Many of us change our filter far too often, usually at an oil change or as soon as it appears a little dirty. In the study it states that “… air filters are designed to actually increase their efficiency by using any initial layer of dust as an added filter layer. New filter efficiency is approximately 98% but actually increases to more than 99% by the end of the filters service life.” It goes on to say “… changing an air filter before the useful service life is achieved can result in premature engine wear.”

The study does state that a filter that has started to plug will affect the performance of the vehicle and you may notice acceleration diminishing but even then there will be little to no effect on your mileage. The study went so far as to block the filter to the point where they were being damaged by the suction with no effect on MPG!