The viscosity of automobile engine oil refers to the resistance when the oil flows. It is usually classified according to the standards set by SAE (Society of Automotive Engineers). The numbers in labels such as "5W-30" or "10W-40" represent low-temperature fluidity and high-temperature viscosity, respectively. The number before W (e.g., 5W) indicates low-temperature performance; the smaller the number, the better the fluidity of the oil at low temperatures, and the stronger the protection for the engine during cold starts. For example, 5W can withstand low temperatures down to -30°C, while 20W can only withstand -15°C. The number after W (e.g., 40) represents the kinematic viscosity of the oil at 100°C; the higher the value, the thicker the oil film at high temperatures, making it suitable for high-load or high-temperature environments. Engine oil is categorized into summer oil (e.g., SAE 40), winter oil (e.g., 5W), and all-season oil (e.g., 5W-30). Japanese and Korean cars, due to their precision-engineered engines, typically require a viscosity grade of 20 or 30; German turbocharged models often need higher viscosity (e.g., 5W-40); older vehicles may benefit from a 40 viscosity grade to compensate for component wear and improve sealing. Additionally, high-viscosity oil is recommended for high-temperature regions or long-distance high-speed driving, while low-viscosity oil is more suitable for short urban commutes or cold climates to enhance fuel efficiency. When selecting engine oil, always prioritize the viscosity grade recommended in the vehicle owner's manual to ensure optimal lubrication and engine longevity.
