The viscosity grade of engine lubricating oil is usually classified according to SAE (American Society of Automotive Engineers). SAE grade indicates the viscosity grade of engine oil. According to SAE classification, lubricants are divided into winter lubricants, summer lubricants and general lubricants in winter and summer. The brands of oils used in winter are 0W, 5w 10w, 15W, 20W and 25W. W stands for winter. The lower the antecedent value of W, the lower its low-temperature viscosity, the better its low-temperature fluidity and the lower the applicable minimum temperature. The grades of oil used in summer are: 20, 30, 40 and 50. The higher the value, the higher the viscosity and the higher the applicable maximum temperature. The brands of general engine oil in winter and summer are 5W/30, 5W/40, 5W/50, 10W/20, 10W/30, 10W/40, 10W/50 and15w respectively.