How to Identify Engine Oil Grades?
4 Answers
Distinguishing engine oil grades is based on quality grades and viscosity grades. The quality grades follow the classification standards established by API, while the viscosity grades are classified according to the standards set by SAE. The classification of engine oil grades is as follows: 1. Viscosity Index: According to the SAE classification method, engine oils are divided into 6 types for winter, 5 types for summer, and 16 types that can be used in both winter and summer. Winter oil grades include OW, 5W, 10W, 15W, 20W, and 25W. The symbol 'W' stands for winter, and the smaller the number before 'W,' the lower the low-temperature viscosity, the better the low-temperature fluidity, and the lower the applicable minimum temperature. Summer oil grades include 20, 30, 40, 50, and 60. The larger the number, the higher the viscosity and the higher the applicable maximum temperature. All-season oil grades include 5W/20, 5W/30, 5W/40, 5W/50, 10W/20, 10W/30, 10W/40, 10W/50, 15W/30, 15W/40, 15W/50, 20W/20, 20W/30, 20W/40, and 20W/50. The smaller the number representing the winter part and the larger the number representing the summer part, the wider the applicable temperature range. 2. Quality Index: According to the API quality classification method, engine oils are divided into the gasoline engine oil series (S series) and the diesel engine oil series (C series). Each series of oils is arranged in alphabetical order (A, B, C, D, E, F) and divided into several grades. The further the letter is in the alphabet, the higher the grade.
Just check the numbers on the oil container and you'll understand. The first letter indicates the type—'S' stands for gasoline engines, while 'C' is for diesel engines. The small number followed by 'W' represents low-temperature fluidity; for example, 5W performs better in cold starts than 10W. The number after the hyphen indicates high-temperature viscosity—40 is thicker than 30. Nowadays, fully synthetic oils like 5W-30 or 0W-20 are mainstream. Back when I first started driving, I researched this—higher numbers mean better high-temperature resistance, but overly thick oil can increase fuel consumption. Your fuel cap or manual will also list the recommended grade. Choosing the right one protects your engine, especially for turbocharged cars, where selecting the correct viscosity is crucial.
I handle over a dozen types of engine oil cans every day. Just remember two key points: the starting letter indicates the grade, and currently, SP grade offers the best performance. The number combination that follows is crucial. For example, in 5W-40, '5W' means it can flow even at -30°C, and '40' represents the viscosity at 100°C high temperature. New cars generally use thin oil like 0W-20 for fuel efficiency, while older cars should use 5W-40 to prevent oil burning. Here's a tip: check the side of the bottle for SAE and API certification marks, which are standard certifications from the American Automobile Association and the American Petroleum Institute. Choosing engine oil also depends on the driving environment. In northern winters, it's best to use oil starting with 0W, 5W is sufficient in the south, and in mountainous areas with high temperatures, a 40 viscosity is more reliable.
Engine oil grades are quite simple to distinguish. The bottle prominently displays characters like API SP/GF-6A, where SP indicates the highest grade. The nearby SAE 0W-20 number combination is what really matters: the number before W indicates better low-temperature performance when smaller, while the larger number after provides stronger high-temperature protection. Nowadays, Japanese and Korean cars tend to prefer thinner 20-viscosity oil, while European and American cars mostly use 30 or 40 viscosity. Last time I used the wrong 40-viscosity oil, my fuel consumption skyrocketed and the fault light came on. The manufacturer's manual explains it clearly—just follow the specifications. Some premium oils even bear the ACEA C5 European standard, offering better cleaning performance than regular oils. They're more expensive but worth it.
