What does 5W mean in motor oil?
2 Answers
The meaning of 5W in motor oil is that 5W is just a temperature grade, representing the minimum applicable temperature of the oil. Below this temperature, the oil becomes very viscous and loses its normal flow capability. The number 5 indicates that the minimum applicable temperature of the oil is -30 degrees Celsius. For example, in the winter outdoors in northern China, if the temperature drops below -30 degrees Celsius, using 5W oil after the vehicle has been parked for a long time can be very troublesome. Oil viscosity specifications: In fact, there are many types of viscosity specifications. Different types of oil have their own characteristics. Taking 5W30 oil as a reference, the letter "W" stands for Winter, while the "5" represents the cold-start performance of the oil. The smaller the number, the stronger the oil's cold resistance, allowing the engine to start easily even at very low temperatures. The last number "30" represents the kinematic viscosity standard at 100 degrees Celsius (between 9.3mm2/s and 12.5mm2/s). Oil classification: High-temperature types for summer use include 20, 30, 40, and 50. The larger the number, the higher the viscosity and the maximum applicable temperature. Low-temperature types for winter use include 0W, 5W, 10W, 15W, 20W, and 25W. The symbol "W" stands for Winter, and the smaller the number before "W," the lower the low-temperature viscosity and the better the low-temperature flow performance, meaning it can be used at lower minimum temperatures. All-season types suitable for both winter and summer include 5W-20, 5W-30, 5W-40, 5W-50, 10W-20, 10W-30, 10W-40, and 10W-50, among others. The smaller the number before "W," the lower the minimum applicable temperature of the oil, and the larger the number after the hyphen, the higher the maximum applicable temperature.
I've been driving for over a decade and often change my own oil. The 5W rating actually indicates the oil's low-temperature fluidity. The 'W' stands for winter, and the lower the number in front, the better it performs in cold weather. 5W oil won't solidify at -30°C and can quickly lubricate the engine during cold starts. Here in the north where winter temperatures drop below -20°C, 5W oil protects the engine instantly at startup, preventing dry friction. If you switch to 10W oil, it might struggle at -25°C. When choosing oil, don't just focus on this number—there's also the high-temperature viscosity rating like 30 or 40, which should match the manufacturer's recommendation. Older cars benefit from thicker oil for better protection, while newer cars run more efficiently with thinner oil for better fuel economy. Even when driving on highways in summer temperatures above 35°C, there's no need to worry about the oil being too thin—just pay attention to the certification standards.
