An engine's air filter cleans the air entering the engine while blocking damaging debris. A dirty air filter restricts air flow, preventing the engine from receiving the amount of clean air it requires to function properly. Over time, a dirty, clogged air filter creates a domino effect: lack of air flow creates a rich air/fuel mixture which can foul the spark plugs, which creates rough idling, engine miss and starting problems, which translates to reduced gas mileage, poor acceleration and decreased engine life.
“I have seen where the customer completely ignored the air filter, and it deteriorated over the years, and the pieces were sucked into the engine, leaving a gaping hole in the filter,” says Ed Nemphos, owner of highly rated Brentwood Automotive in Baltimore. “This allows all kind of debris into the engine, shortening the life of the engine dramatically.”
While a clean air filter is important, there is a balance in order. Air filters should only need to be changed every 12-30k miles, so don't get caught in the dirty air filter scam as an oil-change upsell!
So when does an air filter need to be replaced? Start with your vehicle manufacturer's recommended replacement interval - this will provide the maximum interval length. If your vehicle is driven in unpaved or dusty conditions, filter life will be reduced. Oil changes are a great time to check on your air filter and give it a good shake out. If the filter's filled with debris, is starting to deteriorate, has significantly darkened overall or has dark spots, its time for a fresh filter.