Air filters prevents silica and other solid contaminants by trapping the particles in the fibers that sums up the filter media. Most air filters are made of resin treated cellulose (paper) that is a combination of with synthetic fibers. The typical paper air filter will trap most dirt particles that are 5 to 6 microns in size and larger, along with 80 to 90 percent of the particles down to a couple microns in size. Some of the best premium air filters will prevent anything 2 microns or larger in size or larger, and most particles from 1 to 4 microns in size.
Air filters need to be efficient at trapping dirt, but equally unrestrictive so the engine can breathe normally. For every gallon of fuel burned, 10,000 to 12,000 gallons of air will be drawn through the air filter! That’s a lot of air, and it doesn’t take long for dirt to buildup in the filter, especially if the car is being driven in a dirty environment or on dusty gravel roads.
If the air filter is not replaced, the trapped dirt will close up the pores in the filter and restrict airflow. The filter’s efficiency to trap dirt will actually go up the dirtier it gets. But at the same time, the buildup of dirt will equally make it harder and harder for air to pass through the filter. Consequently, the engine has to suck harder to get the same volume of air. This results in an observable drop in throttle response, engine performance and fuel economy. It can also create carbon monoxide emissions to go up, and may even cause the car to fail a tailpipe emissions test.
The OEM recommended air filter change interval today ranges from 30,000 to 60,000 miles, but these intervals are for ideal operating conditions. A more realistic service interval is to check the filter yearly, and change it every two years or 24,000 miles — or as required depending on driving conditions.
How To Inspect Your Air Filter
To check the air filter, open the air filter housing (which is held shut with clips or fasteners), remove the filter and hold it up to a bright light. If the filter is very dark and transmits little light, it is dirty and needs replacements.
An example of a dirty air filter that needs to be changed
You might want to extend the life of an air filter a bit by tapping the filter against a hard surface to knock dust loose, or by vacuuming the side that prevents the incoming dust. This will knock loose some of the surface dirt, but it cannot completely remove the dirt that is embedded in the fibers in the filter media. Do NOT try to wash a dry paper filter element as this could completely damage the filter.