The function of the oil filter is to filter out metal wear debris, mechanical impurities and oil oxides in the oil. If these impurities enter the lubrication system with the oil, it will increase the wear of engine parts, and may also block the oil pipes or oil passages.
There are two types of oil filters installed before the oil pump and after the oil pump.
The one installed before the oil pump is called the oil filter. Installed after the oil pump and according to its arrangement, there are two kinds of full flow and split flow.

➢Filter
The filter is generally a filter type, which is installed before the oil pump to prevent impurities with large particle size from entering the oil pump. There are two types of filters: floating and fixed.
The floating filter can inhale cleaner oil on the oil surface, but the foam on the oil surface is easy to be inhaled, which reduces the oil pressure and makes the lubrication less reliable.
The fixed filter is installed under the oil surface, and the cleanliness of the inhaled oil is slightly inferior to that of the floating filter, but it can prevent foam inhalation, has reliable lubrication, and has a simple structure. At present, this filter is used in automobile engines.

➢Full flow oil filter
The full-flow oil filter is connected in series between the oil pump and the main oil passage, so all the oil is filtered through it. At present, full-flow oil filters are commonly used in automobile engines.

The filter element of the full-flow oil filter has various forms. At present, most automobile engines use paper filter elements. The oil filter of the paper filter element has two structural forms, one is a decomposable type, just replace the paper filter element when replacing; the other is an integral type, which needs to be completely replaced when replacing.

The full-flow oil filter has a certain service life and should be replaced when it expires. When the filter element of the oil filter is seriously blocked by impurities during the service life, the oil pressure at the oil inlet of the oil filter will increase. When the pressure reaches the specified value, the bypass valve in the oil filter will be opened. At this time, the oil does not pass through the filter element and directly enters the main oil passage. Although the oil is delivered to the various lubricating surfaces unfiltered at this time, it is far better than a lack of lubricating oil.

➢Split flow oil filter
The engine of trucks, especially heavy trucks, generally adopts a full-flow + split-flow oil filter arrangement. The full-flow filter, also known as a coarse filter, is used to filter impurities with a particle size of more than 0.05mm in the oil. The diverter filter, also known as a fine filter, is used to filter out fine impurities with a particle size of 0.001mm or more, and only filter 5% to 10% of the oil supplied by the oil pump.

There are two types of split-flow fine filters, filter type and centrifugal type. At present, the centrifugal oil fine filter is widely used. There is a rotor in the filter, which is supported on a shaft through a rolling bearing. There are two nozzles in the rotor with opposite spray directions. It uses the pressure energy of the lubrication system itself. When the oil enters the rotor and is sprayed from the nozzle, a reaction torque is generated to drive the rotor to rotate rapidly. Under the action of centrifugal force, the oil in the rotor separates solid impurities and accumulates on the inner wall of the rotor. The oil in the center part of the rotor becomes clean and flows from the nozzle back to the oil pan.

The centrifugal oil filter is characterized by stable performance, reliable structure, no filter element to be replaced, as long as the rotor is disassembled regularly, the dirt deposited on the rotor wall can be cleaned and reused, and the service life is very long. Its shortcomings lie in the complex structure, high price, heavy weight, etc., and have high technical requirements for maintenance personnel.