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 only a filter collector and a full flow oil filter
　　
Technical features of oil filter
Filter paper: The oil filter has higher requirements for filter paper than the air filter, mainly because the temperature change of the oil varies from 0 to 300 degrees. Under severe temperature changes, the concentration of the oil also changes accordingly, which will affect the filtering flow of the oil. The filter paper of high-quality oil filter can filter impurities under severe temperature changes to ensure adequate flow.
Rubber seal ring: the filter seal ring of high-quality engine oil is made of special rubber to ensure 100% oil leakage.
Backflow suppression valve: only available in high quality oil filters. When the engine is stopped, it can prevent the oil filter from drying; When the engine is re ignited, it immediately generates pressure and supplies oil to lubricate the engine.
Overflow valve: only available in high-quality oil filter. When the external temperature drops to a certain value or when the oil filter exceeds the normal service life, the overflow valve will open under special pressure, allowing unfiltered oil to flow directly into the engine. In spite of this, impurities in the oil will enter the engine, but it is much smaller than the loss caused by no oil in the engine. Therefore, the relief valve is the key to protect the engine in emergency.