What does the kinematic viscosity of engine oil mean?
2 Answers
The kinematic viscosity of engine oil commonly referred to is the 40℃ kinematic viscosity, which is the main indicator expressing the lubricating performance of engine oil under low shear speed in a normal temperature environment. It can generally be understood as "the viscosity of engine oil during cold starts at normal temperatures." Generally, the faster the engine oil viscosity approaches or reaches the viscosity during warm-up conditions, the less wear it will cause to the engine. More information about engine oil viscosity is as follows: 1. SAE definition: SAE stands for the "Society of Automotive Engineers" in English. It measures the low-temperature start viscosity, low-temperature pumpability, high-temperature kinematic viscosity, and high-temperature shear viscosity of automotive engine oils, among other values. Based on the measured data, engine oils are classified into several grades, which is the SAE viscosity index of engine oil. 2. Engine oil viscosity: The viscosity labeling of automotive engine oil is mainly divided into three parts: W, the number before W, and the number after W. W is the abbreviation for Winter. The number before W indicates the low-temperature fluidity and the applicable minimum temperature value. The smaller the number, the better the low-temperature fluidity of the engine oil, the better the cold start performance, and the lower the applicable temperature. The numbers before W include 0, 5, 10, 15, and 20. 0 indicates the applicable minimum temperature is -35℃; 5 indicates the applicable minimum temperature is -30℃; 10 is applicable to environments above -25℃, and so on. The number after W refers to the kinematic viscosity of the engine oil in a high-temperature environment of 100℃, including 20, 30, 40, 50, and 60. The larger the number, the higher the viscosity of the engine oil, the better the high-temperature protection performance, and the stronger the sealing capability.
The numbers like 5W-30 on the engine oil packaging are the viscosity grades. Let me give you an analogy—it's like comparing honey and water to see which is thicker. The 5W represents the oil's flow speed during cold starts, making it as fluid as water to ensure quick lubrication of every engine corner in winter. The number 30 indicates the oil film thickness at high temperatures, like when the engine temperature soars during highway driving, the 30-grade oil film can steadily coat the metal components. Choosing the wrong viscosity is a no-go: using oil that's too thin in an old car can cause oil burning, while using oil that's too thick in a new car will spike fuel consumption. Last time, my neighbor's Passat used 5W-20 and ended up blowing blue smoke—a classic example. If you're unsure about the grade, check the manual recommendations or have a mechanic measure the engine clearance during maintenance to match the oil—that's the safest bet.
