What is the Definition of Motor Oil Grade?
2 Answers
Motor oil grade refers to the classification of oil's application range. Below are detailed introductions to motor oil grades: Grade Classification: The composition of motor oil grades includes two parts: classification and viscosity specifications. Oil classification is represented by a combination of two letters. Those starting with "S" are for gasoline engines, those starting with "C" are for diesel engines, and those with both "S" and "C" are universal oils for both gasoline and diesel engines. Generally, they are arranged in alphabetical order, with letters further back indicating higher quality grades. The following grade represents oil viscosity; the smaller the number, the better the fluidity in low-temperature environments, and the lower the usable environmental temperature, meaning better engine protection during cold starts. Seasonal Classification: High-Temperature Type: The larger the number representing viscosity at 10 degrees, the higher the viscosity. Low-Temperature Type: "W" indicates use only in winter; the smaller the number, the lower the viscosity and the better the low-temperature fluidity. All-Weather Type: Indicates that the viscosity grade at low temperatures meets the requirements of SAE15W, 10W, and 5W, and the viscosity grade at high temperatures meets the requirements of SAE40 and 50, belonging to the universal type for winter and summer.
I often get asked by friends about what engine oil viscosity ratings mean, such as the common 5W-30 format. Simply put, oil viscosity ratings are based on the SAE viscosity standard, which classifies the fluidity of oil at different temperatures. The 'W' stands for Winter, and the preceding number, like 5, indicates low-temperature viscosity—the smaller the number, the better the fluidity in cold weather, making it easier to start the engine at, say, -30°C. The number after, like 30, refers to high-temperature viscosity—the larger the number, the stronger the protection at 100°C, preventing excessive engine wear. This rating is crucial because it directly relates to engine lubrication effectiveness—choosing the wrong one may lead to hard starts, increased fuel consumption, or shortened engine lifespan. I recommend strictly following the manual's recommendations for new cars, such as modern vehicles often using low-viscosity oils like 0W-20 for improved efficiency, while older cars may use 10W-40 to reduce leakage risks. Also, consider local climate conditions—prioritize lower 'W' numbers for colder winters to ensure smooth daily operation.
