Auto Talk:
Air filters and engine performance

Auto Talk - Air Filters and Engine Performances

For years, motorists have been told to change their engine’s air filter frequently to improve fuel economy. But a recent study by the Oak Ridge National Laboratory has found that this may not have the effect that was previously believed.

On older vehicles with carbureted engines, air filter condition does have an effect on fuel economy. Conventional wisdom has always held that a clogged air filter can cause a 10–15% drop in fuel economy — a figure we have reported in previous Auto Talk columns. However, the new research found that a typical fuel economy decrease is only 2–6%.

On modern fuel-injected vehicles, however, a clogged air filter has no effect on fuel economy — unless it’s so clogged that the engine won’t run at all. What it does affect is the engine’s power output, increasing acceleration times by as much as 1.7 seconds. Dale Kurtz, owner of Courtesy Automotive Service Center, a AAA-Approved repair facility in Colorado Springs, says, "Think of the engine as an air pump. The easier it is to get the air into and out of the combustion chamber, the better the engine will run."

How dirty is too dirty?

In the past, automakers specified mileage intervals for air filter replacement. Today it is more common to replace the filter only when a visual inspection shows it is too dirty. This takes different driving conditions into account.

Visible dirt on the filter is not a sufficient cause for replacement. A more accurate test is to hold the filter up to a 100-watt light bulb. If you can’t see light through more than half of the filter, it should be replaced. If it is still serviceable, dislodge loose debris by tapping the filter against a hard surface.

The light test works only with conventional pleated-paper filters. Extended-life factory air filters on some vehicles do not allow light to shine through, making it difficult to determine their condition visually. These filters are usually replaced at predetermined intervals.

Replacing the filter

Air filter replacement is one of the easiest vehicle maintenance tasks. In many cases it’s a simple matter of popping the hood and opening the case that covers the air filter (it will be recognizable as the largest plastic object in the engine bay). Lift out the old filter and drop in the new one — you’re done! Kurtz suggests, "Add a label to the air filter housing with the date and mileage, to remind you when you last changed it."

Times and technology continue to change, and vehicle maintenance habits need to evolve along with them.

AAA Connection
Need a new air filter? AAA members get a discount on all items at NAPA Auto Parts. Just show your card instore to save.
Visit www.aaa.com/automotive for more car care tips, resources and free online tools like Auto Manager to help you keep track of your vehicle’s maintenance schedule.



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