Air Filter Fundamentals

There is no great mystery to the operation of an internal combustion automobile engine. An automobile engine is essentially an air pump. The pistons and valves work together to draw in and expel air into the combustion chambers as the engine assembly spins round on the crankshaft. The faster this assembly spins, the more air the engine can draw through. Add fuel—in the right amount and spark at the correct moment to this air pump—and the internal combustion equation is complete. Power! With so much air being drawn into the engine from the outside, it is of utmost importance this air enters the engine as clean as possible. It is also important that this flow of air is not restricted in any way.

Front Line Defense
The front line of defense an engine has to fight dirty air with is the air filter. Every molecule of air entering the engine comes through the air filter. Not only does the air filter scrub the incoming air of harmful particulates, it also allows the incoming air to flow freely. Since every bit of crud in the air flowing into the engine stays in the filtration material the air filter is made from, the air filter must be replaced at regular intervals. A dirty and clogged air filter not only loses its ability to clean incoming air, but also offers a restriction to incoming flow. This restriction can result in poor engine performance and loss of efficiency. The good news is that changing an air filter is easy and inexpensive.

Finding the Filter
The first step to changing the air filter is to find it. Open the owner's manual before opening the hood. Find the page that reveals locations of underhood service points and the illustration that shows where the air filter is. If there is no owner's manual, open the hood and look for either a football-sized box opposite the battery, or large circular unit or flat panel box atop the engine. Note locations and types of fasteners, clips, and hold-downs before removing anything.


If you have a digital camera, snap a "before" picture so that all turns out well afterwards. Take care while working not to poke anything into the airflow sensor. Air filters are cheap. Replacement airflow sensors are not. Also take it easy on older, high mileage vehicles. Ham-fisted handling can damage intake hoses and tubes made brittle by years of exposure to underhood engine heat.