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.
Worn Piston Rings
Potential source of engine oil leaking into the air filter housing is due to worn piston rings. The piston rings are installed on the outer edge of the pistons inside the combustion chamber. The rings are intended to create a combustion ratio and permit small amounts of engine oil to continue lubricating the inner combustion chamber during each piston stroke. When rings wear out, they loosen and can cause oil 'blow-by' usually displayed by blue smoke coming from the car's tailpipe while driving. In the early stages of worn piston rings, excessive oil blow-by can cause excessive pressure to build inside the crankcase, which sends more oil through the PCV valve and eventually into the air intake.
Sign of bad Air filter
1. Gas Mileage
Pay attention to your car's gas mileage-a common symptom of a dirty air filter is a decrease in fuel efficiency. Your engine compensates for the lower amounts of oxygen by consuming more fuel to produce enough power. By maintaining a clean, efficient air filter, you can save on fuel costs.
2. Unusual Engine Sounds
When the car is not moving with the engine turned on, you should sense the smooth hum of an efficient engine. If you notice your car is vibrating or hear a coughing or slipping sound, this could be an indication of rough idling taking course. This condition occurs because of a damaged spark plug resulting from a clogged air filter.
3. Air filter appears dirty
If your air filter is brand new, it will look white or off-white. Over time, as it accumulates dust and dirt, it will turn darker in color. When examining your air filter, you should do it in the light of day or with a flashlight, since pollen and dust cannot easily be seen. If you think your air filter is dirty and may need replacing.