What is the Shear Value of Engine Oil?
2 Answers
The shear value of engine oil refers to the oil film strength under high shear conditions at 150 degrees Celsius. A higher value indicates greater strength. In most cases, German cars require engine oil with a shear value greater than 3.5, French cars require a shear value greater than 3.2, while American, Japanese, Chinese, and Korean cars generally require a shear value around 2.9. For aggressive driving or long-distance high-RPM driving, such as frequently driving above 3000 RPM, the requirement for oil shear value should be increased. It is recommended to use engine oil with a shear value greater than or equal to 3.5. For turbocharged, large-displacement cars or SUVs, which are characterized by fast engine speeds and high temperatures, it is advisable to use high-performance fully synthetic engine oil with a shear value greater than or equal to 3.5 and a high viscosity index.
I've been driving for over twenty years, from pickup trucks to sedans, and the oil shear value is a measure of an oil's ability to resist shear forces and maintain viscosity under high temperatures and speeds. Simply put, when the engine is running, the pistons move up and down, and the oil is constantly squeezed and torn. If the viscosity is unstable, the oil film can easily break, causing dry friction between parts. Once, I was on a long-distance trip when my car suddenly became noisy and fuel consumption skyrocketed. After inspection, it turned out the oil's shear resistance was poor. Switching to a high-viscosity, stable oil solved the problem. This is crucial for engine protection, especially when driving at high speeds or hauling heavy loads. It's important to choose good oil and not skimp on quality to avoid costly repairs. Nowadays, I always check the SAE rating on the oil's label to ensure the shear value is reliable—safety comes first, after all.
