Problems a Dirty Air Filter Can Cause

A dirty air filter can trigger problems that include a loss of power (particularly if you have a turbocharged engine), odd engine noises, black smoke out the exhaust and reduced fuel economy. If it’s bad enough, it can even cause the engine not to start or the check-engine light or service engine soon light to go on.

Because the air that’s being filtered can vary tremendously from clean to very dirty, perhaps the best strategy is to inspect the filter regularly rather than simply replacing it at a set interval.

When to Change Your Engine Air Filter

Unlike oil filters and fuel filters, the useful life of an engine air filter (which is different from the cabin air filter) varies greatly based upon the environment in which the car is driven. Also unlike oil and fuel filters, where the “filtering” material is typically housed in a sealed container, an engine air filter can be relatively easily removed from its container for inspection.

While the maintenance schedule on most vehicles gives a mileage interval that’s commonly between 30,000 and 45,000 miles (though there may be a time interval as well) for air-filter replacement, many also include a shorter mileage interval for “severe service.” That’s usually described as regular driving in heavy traffic during hot weather, on unpaved roads or in dusty conditions. Another “life-shortening” possibility is if mice get in the housing and clog the filter with their nesting materials.

Service facilities often recommend changing the air filter more frequently, though that may simply be a ploy to transfer more money from your pocket to theirs. While it doesn’t hurt to change it more often — unless a poor-quality filter is used — it does add unnecessary expense.

Checking Your Air Filter

In most cases, you can inspect the engine air filter yourself without too much trouble.

While old-time air filters were typically round rings housed in a round metal canister on top of the engine, those in modern vehicles are more likely to be cylindrical or flat and housed in a rectangular plastic box in a forward corner of the engine compartment. If the housing that carries the filter isn’t obvious, you should be able to find it in the owner’s manual or online by searching, “Where is the air filter on my [year/make/model].” Some housings are held together with clips, others with screws.

Although the filters themselves are often described as a “paper filter,” they use a type of paper that allows air to flow through while catching dirt and dust. Some may have a foamlike layer on one side that’s intended to stop larger debris from clogging the filter. As the filter paper is typically white when new, anything that looks dirty probably is. Black smudges on the paper are another bad sign.

A common test is to hold the filter up to a light so that the filter is between your eyes and the light. If you can clearly see light coming through the filter, the filter is probably OK. But if the filter is one that has a foamlike pad on one side, this won’t work unless you can easily remove the pad. Note that you may find your car’s air filter to be made of a foamlike material that can be washed and reused, though these are likely to have been substituted for the original filter by a previous owner.

One strategy is to check your air filter a few days before every oil change. That way, if it’s dirty, you’ll have time to buy and change the filter yourself before taking it to the shop for the oil change — likely saving some money over having them do it — or at least knowing whether it’s necessary if they recommend replacement. If you’re charging the oil yourself, you’ll know to purchase an air filter when you buy the oil.

Cars.com by Paul Dolan