(Air intake of Mercedes Benz where air-mass censor is located)
All the engines except electric cars are equipped with air filters before the air reaches the intake valves. The purpose is filter air to avoid the invasion of dust, sand, iron micro dust and other small particles into the engine where the purified air is properly mixed with injected gasoline for ideal burning. Engines burn fuels constantly unless it respires airs from air intake ports. The filtration part is called air cleaner element which is generally made of non-woven fabric. Below is an image of so-called sports air filters that materials are generally different from those of genuine parts.
(Sports type air filters periodically cleaned for V6 engine)
If the air intake contains small particles like dust, the intake valves get dirty and the dust could potentially damage the engine cylinders pistons. In worst case scenarios, dirty air intake can cause engine malfunctions.
It is generally common knowledge that the type of air filters is one of the factory parts that car manufacturers highly recommend. There are two types of air filters; dry type and wet ones. Whether factory parts or OEM (Original Equipment Manufacturing) both are used by auto maintenance garages, OEM are considered affordable compared to factory parts, both can get the job done. Also high performance air filters are sold at relatively high prices because of efficiency and performance.
(The above is factory parts non-woven fabric air filter and the below is sports type)
Air filter of diesel engines should be replaced more frequently than those of gasoline engines’ mainly because of the fact that air filters get dirty faster due to the black smoke more generated as a nature of diesel engines. Gasoline engine’s air intake is controlled by a so-called throttle valve (synchronized with engine) in accordance with acceleration. In case of diesel engines, the amount of air intake is constant and does not vary to the throttle valve resulting in the fact that more air passes through air filters.
How often the air filter should be changed?
The replacement cycle of air filter is every 2 years or every 40,000km in general. However, it totally depends on the conditions of roads and how you use the automobiles.
For example, under the conditions of dirty air exposed to the automobiles such as driving in congested routes and air-polluted circumstances, the replacement cycle diminishes drastically. Under such conditions, we strongly recommend to replace air filters every year or 20,000km at least every 30,000km.
To learn more about changing air filters, check out: http://blog.beforward.jp/auto-parts/major-advantages-replacing-air-filters.html