Engine Lub oil will be polluted by the parts wearing particle and outer impurity which enters into the engines, also for being subjected to heat radiation of the hot parts; it will be oxidized, and produces acidic material which can dissolve in oil and colloidal deposit which is not soluble. These impurity arid contamination is very harmful to the engines, if they are not be filtered, the hard particle in the oil will accelerate parts to abrade, and jam the oil passage. The acidic material will bring the corrosive abrasion of the alloy bearings. The colloidal deposit will lead the pistons and piston rings and valves and valve stem guide to cement, even the engine can not run, and shorten the oil drain interval. It is said that if the total valve of the solid contamination in the oil is less than 0.15%, the harm to the engine is limited, if this valve is more than 0.5%, the harm to the engine is very serious. Therefore, the oil filters should be assembled in the lubrication system of the engine ALL.