What is the Engine Oil Viscosity Grade Chart?
4 Answers
The viscosity grade of engine oil is closely related to the vehicle model and local temperature. Below is an introduction to vehicle models and grades: 1. Vehicle Models: Japanese cars primarily use low-viscosity oil, while German cars primarily use high-viscosity oil. 2. Grades: (1) 0W suitable temperature: -35°C (polar regions). (2) 5W suitable temperature: -30°C (northeast and northwest regions). (3) 10W suitable temperature: -25°C (central and southwestern parts of northern China). (4) 15W suitable temperature: -20°C (central and southwestern parts of northern China). (5) 20W suitable temperature: -15°C (areas south of the Yellow River and north of the Yangtze River). (6) 25W suitable temperature: -10°C (subtropical regions).
I found that the engine oil viscosity grade chart is actually the most important reference standard when choosing oil, just like checking sizes when buying clothes. This chart has SAE designations such as 5W-30 combinations, which I always refer to during oil changes. The first number, like 5W, represents low-temperature fluidity, which is especially critical for cold starts on winter mornings; the latter number, 30, indicates viscosity at high temperatures, preventing engine overheating during summer driving. Last month, while helping a friend check his car, I noticed he was using 20-weight oil, but his car was already ten years old. Older engines with increased clearances require 40-weight oil to form sufficient oil film protection. Using the wrong viscosity can easily lead to abnormal wear. I recommend checking the vehicle manual for the recommended grade before maintenance. New cars generally use low-viscosity oil for fuel efficiency, while older cars can appropriately increase viscosity.
In our auto repair shop, the most commonly used method to determine oil performance is the oil viscosity grade chart. The core of this chart is the SAE rating, which divides viscosity into winter and summer indicators. Breaking it down: the smaller the number before the W, the better the cold resistance, such as 0W oil that remains fluid even at -40°C; the larger the number after the W, the better the high-temperature protection. Once, I encountered an off-road vehicle whose owner often drove on mountain roads, so I chose 10W-40 for it, as the higher high-temperature viscosity can handle the engine's heavy load. Nowadays, most new cars come with low-viscosity 0W-20 oil from the factory, which can save some fuel, but for older German cars, 5W-40 is still recommended. The worst scenario is when car owners use the wrong oil. I once saw a Mercedes using 5W-20, which resulted in camshaft damage.
The engine oil viscosity grade chart is essentially the identity tag of the oil. Codes like 5W-30 actually indicate the temperature adaptability range. For example, my car uses 0W-20 oil, which can still start at -30°C in winter. The values in this chart are determined through laboratory tests: the low-temperature number reflects cold-start performance, while the high-temperature number indicates viscosity at 100°C. Different viscosities suit different scenarios: for frequent highway driving, it's recommended to use oils with a high-temperature viscosity of 30 or above, while 20 is sufficient for short commutes. The most crucial point is not to misuse oils across grades—using 40 viscosity oil in Japanese cars, for instance, can increase fuel consumption. Nowadays, I always check the owner's manual before changing oil, sticking to the manufacturer's recommended grade for the safest bet.
