Your car or truck burns around 12,000 gallons of air for every gallon of gasoline it burns, according to the Filter Manufacturers Council. Do that math—if your vehicle gets 20 MPG, that’s 240,000 gallons of air for every mile you drive. Why do we care? Unfortunately, that air is carrying a fair amount of plain old dirt, swept up off the road by traffic and the breeze. And a lot of that is silicon dioxide: common beach sand. Silicon dioxide is what’s used to make sandpaper. And it has no business inside your engine, because it will inevitably wear out expensive components like valves, pistons and bearings which is why its important to follow the guide below to know when you need to change your air filter. The air filter’s job is to let in the air with as little restriction as possible, while keeping out as much dirt as feasible.
As the filter accumulates dirt, the restriction to flow grows cumulatively, making your engine work harder to ingest air. The engine’s fuel injection system will, of course, correct the amount of fuel mixed with the air to keep the proper proportion of fuel to air. The result of that is a reduction in maximum horsepower, although the reduction will be miniscule. More importantly, the engine has to expend some energy to suck air through an increasingly more restrictive filter, and that eventually will affect fuel economy.
So, how often do you really need to change your air filter?
You may be thinking your best bet is to remove the filter, and clean or change your air filter regularly, right? Not so fast. It’s more complicated than that.
- A fresh filter is actually less efficient than a seasoned filter, as trapped dust particles ultimately become part of the filter medium, trapping smaller and smaller particles as time goes by. And modern filter elements and air cleaner designs are engineered to trap a lot of dirt before the restriction grows to a point where it matters.
- The time-honored practice of removing an air filter, beating the dust out of it on the corner of the shop, and reinstalling it have passed. Attempting to clean a filter will leave the “clean” side contaminated with dust, which winds up – guess where – inside your engine. It’s best practice to replace the filter when it gets dirty. If you’re going to do it yourself, while you have the air cleaner opened up, take a damp shop rag and clean as much dust out of the housing as you can before carefully installing a new filter. Make sure the seal around the perimeter is correctly installed and all of the clamps are tight, lest dirt sneak past into your engine.
Exactly how often do you need to change your air filter? That’s a simple answer—it’s in your owner’s manual.
- If you live on a dusty road, or in places where seasonal pollen accumulation loads up filters prematurely, maybe a little more often. I like to write the date and mileage of the filter replacements, oil, fuel, air and cabin, in the back of the owner’s manual.
- If you’d rather leave the air-filter change to a mechanic, check out Openbay, which will find a local one for you, and will keep track of your air filter change (along with all your repair and maintenance) online, so you don’t have to bother scribbling notes in the back of your manual.
Mike Allen – guest writer for Openbay. He’s an ASE-certified mechanic, longtime former editor of Popular Mechanics, and world-record-holding race-car driver. For more on Mike, check out his bio here, and find him on his own site, Saturday Mechanic