Manufacturers agree that one of the most important issues affecting engine air filters is something fleets can have complete control over: using restriction gauges, or monitors, to determine when it's time to replace the filters. In practice, however, many fleets change air filters either when they “look” dirty or when they've been in service for a given number of miles. The problem with these methods is that people end up changing filters too frequently.

While cost is the first consequence that comes to mind, there are other more serious ramifications when you change air filters before you need to. In fact, doing so can actually put your engine at higher risk for contamination. As Baldwin Filters points out, an engine is most susceptible to contamination from dirt, dust, etc., when it's exposed to the environment during a filter change. It stands to reason that the more often you do this, the greater your chances of contaminating the engine.

Another option is disposable air cleaners, where the entire assembly is replaced, rather than just the filter element. For example, Farr's Eco-LL products are self-contained units that eliminate the issue of contamination — “engine dusting” — during filter replacement.

Then there's the misconception that air filters are most efficient when they're brand new. It's really just the opposite. Fleetguard/Nelson explains that an initial buildup of dust and dirt serves as a kind of second filter, so that up to a point, filters become more efficient the longer they're in place. To put it another way, if you replace them too often, you're minimizing the amount of time engines can benefit from filters functioning at maximum efficiency, Fram points out.

Leaving filters in place too long presents a different kind of problem. Loss of power and a decrease in fuel economy are two possible negative outcomes when engine air filters become too clogged with dirt and grime. And on the extreme end of the spectrum, according to Wix, a filter can become so restricted that it's actually crushed, with parts breaking off and getting sucked into the turbo, causing damage to the engine.

Wix also mentions that since newer turbocharged engines designed to meet stricter emissions criteria are especially sensitive to intake dirt, it's crucial that filters function at peak efficiency.

By measuring the differential pressure across the filter element, restriction gauges can tell you whether you're getting the right amount of airflow, or whether the filter's becoming too plugged to function properly, Baldwin explains. Using these monitors to determine when to change your air filters eliminates the mistake of doing so prematurely.

Wix points out that at about $20-$30 apiece, restriction gauges are relatively inexpensive, especially given the benefits they provide. They also recommend keeping the gauge itself clean by taking it out and vacuuming it from time to time. Gauges can be mounted on the dash or directly on the air filter housing.

As far as type is concerned, radial filters have become standard for most new on-highway and construction vehicles. Designed primarily for serviceability, these filters are easier to install and remove than those with the standard metal cap design. In addition, the improved sealing mechanism diminishes the likelihood of leaking, resulting in enhanced performance. Most manufacturers offer retrofit kits for the aftermarket so that fleets with older vehicles can switch to radial-seal filters if they want to.

In general, paper media is still considered to do the best job for the money in over-the-road applications. But the industry will continue to see an increase in filters made of a combination of cellulose and synthetic media, especially for applications that require longer life, longer serviceability and higher efficiency.

Filter makers continue to face the challenge of developing units that are smaller, yet maintain or even improve performance levels. This stems in part from a trend to more aerodynamic vehicle design in an effort to improve fuel economy. According to Fleetguard/Nelson, manufacturers have responded by developing innovative technologies to create media that are more efficient.


Baldwin Filters 262
Kearney NE

Donaldson 263
Minneapolis MN

Farr Co. 264
Memphis TN

Fleetguard/Nelson 265
Nashville TN

Fram/Honeywell 266
Danbury CT

LuberFiner/Champion 267
Albion IL

Racor/Parker Hannifin 268
Modesto CA

Wix Filtration/Dana 269
Gastonia NC