What is the Job of the Air Filter?

The air filter is designed to capture debris, dirt, and other contaminants — but not oil. Occasionally, when a local service mechanic replaces an air filter, the technician will indicate that engine oil has been found; either inside the air filter housing or embedded inside the used filter. While oil finding its way into the air filter is not typically a sign of catastrophic engine failure, it should definitely not be neglected.

The air filter on most modern combustion engines is located inside an air intake housing, which is installed on the top of the engine. It is attached to the fuel injection system (or a turbocharger) and designed to efficiently transport air (oxygen) into the fuel system to be mixed with fuel before it enters the combustion chamber. The main duty of the air filter is to remove dirt particles, dust, debris, and other impurities before the air mixes with liquid gasoline (or diesel) to become a vapor. When the air filter becomes clogged with debris, it can cause the engine’s fuel efficiency and power output to decrease. If oil is found inside the air filter, it can also significantly impact the engine’s performance.