How to Identify Oil Viscosity?
2 Answers
The viscosity of engine oil can be determined by its grade, which consists of two parts: the classification and the viscosity specification. The oil grade typically indicates both viscosity and quality. The viscosity of lubricating oils is often labeled using SAE (Society of Automotive Engineers) grades. Here are specific details about gasoline engine oil viscosity specifications: 1. The number following the oil classification indicates its viscosity specification. For example, in grades like "15W-40" or "5W-40," the "W" stands for Winter. The smaller the number before the "W," the better the oil's low-temperature fluidity, meaning it can be used in lower environmental temperatures and provides better engine protection during cold starts. 2. 5W indicates resistance to external temperatures as low as -30°C, while 20W can withstand temperatures down to -15°C. The number after the "W" represents the oil's kinematic viscosity at 100°C—the higher the number, the higher the viscosity. 3. A value of 40 means the kinematic viscosity standard at 100°C is between 12.5mm²/s and 16.3mm²/s.
Last time I took my car for maintenance, I noticed the oil can was labeled 5W-30. The mechanic said the number before the W represents low-temperature fluidity, and since I'm in the northeast, I must use oil starting with 0W, which can start the engine even at -30 degrees Celsius in winter. The number 30 after the W indicates high-temperature viscosity. For my old Passat, I need to use 40 viscosity oil, otherwise, it's prone to burning oil. Before changing the oil, I always feel the old oil to check its stickiness. If it's too thin or too thick, it's time for a change.
