C is for diesel fuel. Starting with CA, CB, CC, CD, CE, CF, CF-4, CG-4, CH-4, CI-4 and CJ-4, the later the letter, the higher the quality grade of the oil. CD grade oil is sufficient for general diesel engines, and supercharged diesel engines require a slightly higher quality oil. -4 indicates that the oil is suitable for four levels of diesel fuel grading: 1, API indicates that the American Petroleum Institute (referred to as) on the oil quality rating standards 2, s indicates gasoline oil, l indicates the grade, APISA, SB, SC, SE, SF3, c indicates diesel fuel. f indicates that the grade, starting from APICA, CB, CC, CD, CE, CF, CF-4, CG-4, CH-4 The higher the letter, the higher the grade of the oil; 4, SAE gives the American Society of Automotive Engineers (abbreviation) on the viscosity grade of lubricants; 5, 5W indicates the temperature range of the oil, 0W, 5W, 10W, 15W, 20W, 25W, etc. indicates that the smaller the number, the better the low-temperature mobility, the better the low-temperature conditions; 6, 40 indicates that the oil in 100 ℃ under the viscosity of the grade There are SAE20, 30, 40, 50, 60, the larger the number the higher the viscosity. 5W50 is generally known as multigrade oil, indicating that the viscosity of the oil at low temperatures meets the requirements of 5W, and the viscosity at 100 ℃ meets the requirements of No. 40. 7, 5W40SL/CF 'indicates that the oil has good low-temperature liquidity, meets the requirements of 5W, and the viscosity is in the range of No. 40 at 100 with the performance of gasoline engine SL grade and Diesel engine CF grade performance, winter and summer general, north and south general, for pure synthetic lubricants.