The Filter Minder® reads the restriction in the air induction system. Air filters usually have low restriction for most of their service life, and the position indicator will not move very much. Then, as the air filter reaches the end of available service life, filter restriction increases rapidly, and the position indicator of the service indicator will move faster towards the red zone. (See Side Bar)

Although an air filter may look dirty, it is impossible to tell the true condition by visual inspection. An air filter that looks dirty may have much of its service life remaining. Air filters have low restriction for most of their service life, then restrict rapidly at the end. It is best to leave the air filter in place until restriction is noticed on the air filter service indicator.

Air filter service life depends on operating conditions. An air filter may restrict in a few hours/miles, or last several hundred hours (sometimes 100,000 miles or more). Monitoring the air filter with a Filter Minder® service indicator takes the guesswork out of air filter maintenance.

Fuel consumption remains constant as air filter restriction increases until it reaches a certain point. Testing by independent companies suggests a slight increase of fuel consumption with a diesel engine when air filter restriction reaches 17-18 inches water vacuum. However, the fuel consumption may not be severe.

The 17-18 inches restriction is only seen at full load conditions, which may be an infrequent condition. Full load condition includes hard throttling, pulling a trailer, or passing another vehicle. Air filter restriction reduces when these conditions end. The engine may be operating most of the time at lower restriction levels cruising at highway speeds, which would not affect fuel consumption. If there are concerns about excess fuel consumption, the air filter can be changed at lower restriction levels.