What do the numbers and letters on engine oil mean?
4 Answers
The numbers and letters on engine oil represent the following: Taking 5W30 as an example, the number before W indicates the freezing point temperature. The smaller the number, the lower the viscosity, the better the low-temperature fluidity, and the lower the applicable temperature. The number after W represents the kinematic viscosity of the oil at 100 degrees Celsius. The smaller the number, the lower the viscosity, the better the low-temperature fluidity, and the lower the applicable temperature. When using engine oil, ensure that the oil grade is correct and that the oil is genuine. Using counterfeit or substandard oil can damage the engine. Engine oil, also known as engine lubricant, serves to lubricate and reduce friction, assist in cooling, seal against leaks, prevent rust and corrosion, and provide shock absorption for the engine.
I've been driving for over twenty years and often get confused by the letters and numbers on engine oil bottles. For example, 5W-30: 'W' stands for winter, and the smaller the number before it, the smoother the cold start, even at -20°C. The 30 after represents viscosity at high temperatures, with higher numbers indicating better engine wear resistance. Different seasons require different oils: use 0W or 5W in winter to prevent freezing and starting issues, and 40 in summer for better heat resistance. Always check the SAE standard number for reliability. Using high-viscosity oil improperly can increase fuel consumption and damage parts. It's best to consult the manual and follow the manufacturer's recommendations. Don't cheap out on off-brand oils. Regular oil changes and maintenance are key. I've seen too many people waste money on engine repairs due to using the wrong oil.
Engine oil grades like 5W-40 are super interesting! The number before 'W' indicates low-temperature fluidity test value - 5 means it can flow at -30°C, while 0W performs even better. The number after the hyphen (e.g., 40) refers to kinematic viscosity at 100°C - higher numbers mean thicker oil film for better high-speed engine protection. API ratings like SN or SP represent emission standards, while ACEA C3 suits vehicles with particulate filters. Oil selection depends on driving habits: use low viscosity for stop-and-go traffic (better fuel economy), high viscosity for aggressive driving. Southern regions can use 5W-30 year-round, while northern winters require 0W. Don't blindly trust 'full synthetic' claims - check actual test parameters, and never exceed 8,000 km oil change intervals to prevent severe carbon buildup.
I always worry about using the wrong engine oil and damaging my car, so I carefully check the labels every time I change the oil. For example, in 10W-40, the number '10' before the 'W' indicates winter suitability—the lower the number, the easier it is to start the engine in cold temperatures, making it ideal for extreme winter conditions in the north. The '40' represents the high-temperature protection grade; the higher the number, the thicker the oil remains at high temperatures, ensuring better protection. For daily commuting, oils with a viscosity of 20-30 are sufficient and more fuel-efficient, while high-displacement vehicles are recommended to use 40 or above. Also, look for the API certification to ensure cleanliness, and older cars should avoid low-ash oils marked with 'C.' The owner's manual is the most reliable guide—my SUV has been running on the recommended 5W-30 for 60,000 kilometers, and the engine still runs quietly.
