Automobile engines are basically internal combustion engines, mainly using gasoline and diesel fuel. As a fuel, there must be certain requirements for the quality and cleanliness of the oil. Due to refining and processing reasons, the finished fuel contains a certain amount of impurities, water and colloid. The function of the fuel filter is to filter out these impurities in the fuel and supply clean fuel to the engine. If the fuel is not filtered well, the impurities in the gasoline will easily block the small holes in the carburetor, causing the carburetor to work poorly and the combustible mixture to become thinner; the impurities in the diesel will enter the injection pump, which will easily accelerate the wear of the precision parts and reduce the pump oil pressure. If the water and colloid in the fuel enter the cylinder, the combustible mixture will burn poorly and the power of the engine will decrease. The gasoline filter generally has only one stage, installed between the gasoline tank and the gasoline pump or between the gasoline pump and the carburetor. Since there are three precision parts in the diesel engine supply system, the diesel oil has a high cleanliness requirement and the colloid content in the diesel oil is high. In order to improve the filtration efficiency, the diesel oil filter generally has two or more stages, which are divided into diesel oil coarse and fine filters, also known as oil-water separators and diesel oil fine filters. They are installed between the diesel oil tank and the oil pump, and between the oil pump and the injection pump. Some diesel engines are also equipped with a sedimentation cup to precipitate water and impurities in the diesel oil.