Does an engine air filter’s performance improve as it becomes dirty? Under dusty conditions some operators blow out their air filters daily, while others extend the interval with the attitude that, “A dusty filter cleans air better than a clean filter.”
Alex Reynolds, managing director of a major air filter manufacturer, agrees with the theory but disagree with the practice.
“An air filter’s efficiency at stopping contamination rises as the holes in the media get filled with dirt particles,” he says. “But that improved efficiency in stopping particles comes at the cost of permeability. The less permeable an air filter is, the less air can move through it, and the less air an engine gets, the less power it has. Yes, a dirty filter can clean better, but a dirty filter also decreases horsepower.”
Horsepower reduction due to restricted air filters is initially subtle but can become significant. Everybody is very conscious to change fuel filters when their machines become “doggy.” It’s not a bad idea to check and clean the air filter at the same time.
When cleaning air filters, replace the filter if the metal screen around the outside and inside of the pleated media is creased, bowed or deformed. Those screens maintain the cylindrical specifications of the filter, which is critical for a proper seal in the air cleaner housing.
A dented screen may pull one end of the filter down slightly, reducing the contact area of the sealing surfaces on the ends of the filter and allow contaminated air into the engine.
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