When the engine is running, with the operation of the oil pump, the oil with impurities enters the oil filter from the oil inlet on the bottom plate assembly of the oil filter, and passes through the check valve to the outside of the filter paper for filtering. Under the action of the oil pressure, the oil continuously passes through the filter paper and enters the center tube, while the impurities in the oil remain on the filter paper.

The oil filter is located in the engine lubrication system. The upstream of the oil filter is the oil pump, and the downstream is the parts that need to be lubricated in the engine. The function of the oil filter is to filter out harmful impurities in the oil, and to supply the crankshaft, connecting rod, camshaft, supercharger, piston ring and other moving parts with clean oil to play the role of lubrication, cooling and cleaning, thereby extending the life of these parts.

The oil filter is mainly composed of filter paper and housing, as well as auxiliary components such as sealing ring, support spring, and bypass valve. From the appearance, we see the oil filter as a whole, the filter paper, bypass valve and other parts are invisible. In reality, there are two types of oil filters: coarse filters and fine filters. The lubrication system also has two filtering methods: full flow and split flow. The coarse oil filter and the fine filter correspond to the full-flow type and the split-flow type respectively.