What does 10w40 mean for car engine oil?
4 Answers
Car engine oil 10w40 refers to the viscosity grade of the oil. The number 10 indicates the minimum applicable temperature of the oil is -25 degrees Celsius, W stands for all-season use (both summer and winter), and 40 represents the high-temperature viscosity of the oil. The higher this number, the thicker the oil is at high temperatures. W stands for winter, and the smaller the number before it, the better the low-temperature fluidity of the oil, indicating a lower usable ambient temperature and better engine protection during cold starts. The number after W is an indicator of the oil's high-temperature resistance. The larger the number, the better the oil's protective performance at high temperatures.
The oil I've been using in my car is 10w40, which actually represents the viscosity characteristics of the oil. The W stands for winter, and the number 10 before it indicates low-temperature fluidity. During cold starts in winter, the oil won't be too thick and can still flow normally at around -25 degrees Celsius. The 40 after it represents high-temperature viscosity. At the engine's operating temperature of 100 degrees, it has higher viscosity and can form a sufficiently thick oil film to protect the engine. This type of oil can be used all year round and is especially suitable for ordinary family cars and regions with significant temperature variations. When choosing oil, you should refer to the vehicle's manual. Older cars with larger engine gaps are better suited for higher viscosity oil, while newer cars should use lower viscosity oil for better fuel efficiency. Remember to change the oil on time; otherwise, even the best viscosity rating won't help.
In repair shops, 10w40 engine oil is quite commonly seen. The first number, 10, indicates the oil's viscosity grade at low temperatures—the smaller the number, the better the fluidity in cold conditions. The 40 after the W represents high-temperature viscosity; a higher number means the oil is thicker at high temperatures, offering better protection. In simple terms, this means easier engine starts in winter and a thicker oil film for protection in summer heat. This viscosity grade suits most naturally aspirated engines, especially family cars that have run 70,000 to 80,000 kilometers. However, note that turbocharged vehicles or newer engines might require lower-viscosity oils like 5w30. When changing oil, don't just look at the viscosity grade—also check if the certification standards match your engine.
10W40 is the SAE viscosity grade for engine oil. The number 10 before the W indicates its flow performance at low temperatures, maintaining fluidity during startup at -25°C. The number 40 represents the kinematic viscosity of the oil at 100°C, with higher values indicating stronger oil film. For daily driving, this grade balances cold-start protection and high-temperature wear resistance. It's quite suitable for car owners in northern regions, as it doesn't thin out in summer or thicken in winter. However, always refer to your vehicle's manual when selecting oil, as requirements may differ between German and American cars. Also, pay attention to the oil's performance level, such as API SP/SN certification, for better assurance. Timely oil changes are more important than obsessing over viscosity grades.
