What Do the Numbers in Engine Oil Specifications Represent?
2 Answers
Engine oil specification numbers represent grading and viscosity ratings. For example, in 5W40, the 'W' stands for winter, and the smaller the number before it, the better the oil's low-temperature fluidity, indicating a lower usable ambient temperature and better engine protection during cold starts. For instance, 5W indicates resistance to external temperatures as low as -30 degrees Celsius. The number after the 'W' represents the oil's kinematic viscosity at 100 degrees Celsius, with higher numbers indicating higher viscosity. Engine oil, also known as engine lubricant, serves to lubricate and reduce friction, assist in cooling, seal against leaks, prevent rust and corrosion, and cushion against shocks, earning it the nickname 'the blood of the car.' Engine oil consists of two parts: base oil and additives. The base oil is the main component of the lubricant, determining its fundamental properties, while additives compensate for and improve the shortcomings of the base oil, imparting certain new characteristics, making them an essential part of the lubricant.
The numbers in oil grades actually represent the viscosity rating. In a format like 5W-30, the first number with a 'W' (e.g., 5W) indicates the low-temperature viscosity. 'W' stands for winter, and the smaller the number, the thinner and more fluid the oil is in cold weather, ensuring smoother cold starts for the engine. The second number, 30, represents the high-temperature viscosity, indicating the thickness of the oil film when the engine is hot. A larger number offers stronger protection, but it's not necessarily better—it depends on the vehicle model. The SAE standard tests these properties at specific temperatures. Choosing the right viscosity can reduce engine wear and extend its lifespan. After years of studying motor oil, I've found that ignoring these factors can lead to increased fuel consumption or noise. It's crucial to refer to the manual when changing oil and not to randomly select a grade.
