The gasoline is not pure. There are many impurities in it. Also, when you open the fuel tank cap during refueling or maintenance, impurities will enter. The filter screen in the fuel tank can only filter large impurities. It is powerless for small particles.

Oil filter, also known as oil grid. It is used to remove dirt, metal particles, carbon deposits, soot particles and other impurities in the engine oil to protect the engine. The oil filter can be divided into full flow type and partial flow type. The full flow filter is connected in series between the oil pump and the main oil passage, so that all lubricating oil entering the main oil passage can be filtered.

The shunt cleaner is connected in parallel with the main oil passage, and only part of the lubricating oil is sent by the filter oil pump. During engine operation, metal wear debris, dust, carbon deposit oxidized under high temperature, colloidal sediment, water, etc. are constantly mixed with lubricating oil. The role of the oil filter is to filter out these mechanical impurities and gums, keep the lubricating oil clean and extend its service life.

The oil filter shall have the characteristics of strong filtering capacity, small flow resistance, long service life, etc. In general, several filters with different filtering capacities are installed in the lubricating system - filter collector, coarse filter and fine filter, which are respectively connected in parallel or in series in the main oil passage. (The one in series with the main oil passage is called full flow filter, and all lubricating oil is filtered by the filter when the engine is working; the one in parallel is called split flow filter).

One coarse filter is in series in the main oil passage, which is full flow type; The secondary filters are connected in parallel in the main oil passage and are of split flow type. Modern car engines are generally equipped with a collector and a full flow oil filter. The coarse filter removes impurities with a particle size of more than 0.05mm from the engine oil, while the fine filter is used to remove fine impurities with a particle size of more than 0.001 mm.