What do the markings on engine oil represent?
3 Answers
Engine oil has two types of markings: SAE and API, each with different meanings. SAE Marking: "5W-30" is an example of an SAE marking. The "W" stands for Winter. The number before the W indicates the oil's fluidity at low temperatures—the smaller the number, the better the fluidity in cold conditions. The number after the W represents the oil's viscosity at 100 degrees; a higher number means the oil maintains better viscosity at high temperatures. API Marking: "SN" and "SL" are examples of API markings. The "S" stands for gasoline engines. Generally, the letter following the S indicates the oil's grade—the further the letter is in the alphabet, the higher the grade, meaning the oil performs better.
I've been driving for twenty years, and the matter of oil viscosity grades really needs to be explained properly. Take the numbers like 5W-30 for example - the 'W' in 5W stands for winter, and the smaller the number, the better the low-temperature fluidity. In places like Northeast China where temperatures drop to -30°C, you should use oil that starts with 0W. The number 30 represents high-temperature viscosity - the larger the number, the thicker the oil film. Older cars or those frequently driven at high speeds are better suited for 40 viscosity. However, higher viscosity isn't always better. Nowadays, new cars use thinner 20 viscosity oil, which saves fuel and protects the engine. Last time, my friend insisted on putting 40 viscosity oil in his new car, and it ended up increasing fuel consumption by more than half a liter and made acceleration sluggish. The key to choosing oil is to follow the maintenance manual requirements, and it's best to check if the oil viscosity grade is correct before seasonal changes.
Helping car owners choose engine oil every day at the auto repair shop, the rating mainly depends on temperature and vehicle condition. The number with 'W' on the left indicates low-temperature performance, like 0W can flow at -35°C, while 5W only needs to withstand -30°C. The number on the right is the viscosity grade at 100°C; Japanese cars generally require 20 or 30, while German turbocharged cars often use 30 or 40. Now that it's summer with high temperatures, if the oil light on the dashboard occasionally flashes, it might be due to insufficient viscosity, and it's time to switch to 40-weight oil. Last time, a BMW owner used the wrong 20-weight oil, and the engine sounded like metal clanging. Remember to check the API label; SN grade offers much better cleaning performance than SM.
