What Does the Engine Oil Model Number Represent?
2 Answers
Engine oil model numbers represent the following: An oil that starts with 'S' indicates it is for gasoline engines, while an oil that starts with 'C' indicates it is for diesel engines. If both 'S' and 'C' are present, it means the oil is suitable for both gasoline and diesel engines. The viscosity of engine oil is often indicated using the SAE grade. For example, in SAE5W40, the number before 'W' indicates the oil's low-temperature fluidity—the smaller the number, the better the fluidity at low temperatures, meaning it can be used in colder environments. 5W means the oil can be used at temperatures as low as -30 degrees Celsius. The number after 'W' indicates the oil's high-temperature performance—the higher the number, the better the oil's protective performance at high temperatures. 40 indicates that the oil's kinematic viscosity at 100 degrees Celsius is between 12.5 and 16.3.
Last time I helped my neighbor uncle check the motor oil container, I realized the oil grade actually hides a lot of information. For example, in 5W-30, the first number 5W represents low-temperature fluidity—the smaller the number, the better it resists freezing, capable of pumping even at -30°C, making it especially suitable for folks in Northeast China. The 'W' in the middle stands for Winter, and the 30 at the end indicates high-temperature viscosity, which determines the thickness of the oil's protective film when driving at high speeds. Back when I worked as a mechanic, I often saw car owners using the wrong viscosity, like forcing 20-weight oil into German cars, resulting in oil burning and blue smoke. Also, the SP/SN label on the container indicates the quality grade—new cars nowadays should always choose SP-grade oil, as it can prevent timing chain elongation. Remember three key factors when selecting oil: the low-temperature number depends on regional temperatures, the high-temperature number depends on the car model’s requirements, and the letter grade should never be lower than the manufacturer’s manual specifies.
