Why is oil called 5W30?

5W30 is the SAE viscosity grade designation for motor oil, consisting of two parts: low-temperature fluidity (5W) and high-temperature viscosity (30). The "W" stands for Winter, and the number 5 indicates that the oil can maintain good fluidity at -30°C, ensuring rapid lubrication of engine components during cold starts-the smaller the number, the better the low-temperature performance. The number 30 refers to the kinematic viscosity of the oil at 100°C; the larger the value, the stronger the high-temperature protection, as it can form a stable oil film when the engine operates at high temperatures. This all-season motor oil is suitable for environments ranging from -30°C to 35°C, particularly for precision engines in Japanese and Korean vehicles and small-displacement turbocharged models, such as the Toyota Vios or Honda City. Note that for older vehicles with over 100,000 kilometres on the odometer, upgrading to a 40 viscosity oil may be advisable to improve sealing performance. When selecting oil, balance fuel efficiency with engine protection, avoiding excessive viscosity that could increase fuel consumption.