What Does the Engine Oil Model Number Mean?
3 Answers
Engine oil model numbers consist of two parts: the classification and the viscosity specification. The number following SAE indicates the viscosity value of the engine oil, while the number following API indicates the quality level of the engine oil. Generally, the engine oil model number represents viscosity and quality. As the "blood" of the engine, engine oil not only lubricates and cools the engine but also provides anti-corrosion and anti-wear protection. Here are some details about engine oil model numbers: 1. The viscosity of lubricating oil is often marked using the SAE grade, where SAE is the abbreviation for the Society of Automotive Engineers. For example, 10W-40 is its SAE standard viscosity value. This viscosity value indicates that the engine oil is a multi-grade lubricant. The "W" stands for WINTER, the number before the "W" represents the pour point temperature, and the number after the "W" represents the kinematic viscosity of the engine oil at 100°C. The higher the number, the higher the viscosity. 2. API engine oils are divided into two categories: those starting with "S" represent oils for gasoline engines, and those starting with "C" represent oils for diesel engines. If both letters are present, it indicates that the engine oil is suitable for both gasoline and diesel engines.
When you see engine oil grades like 5W-30, let me explain it from the perspective of a driver with over a decade of experience. The 'W' stands for winter, and the number before it indicates the low-temperature viscosity rating. The smaller the number, the better the oil flows at low temperatures. For example, 0W can still flow at -35°C, while 5W flows at -30°C. The number after the 'W' represents the high-temperature viscosity rating, where 30 indicates the oil film thickness and lubrication capability when the engine is running at high temperatures. Simply put, the combination of these two numbers represents the oil's applicable temperature range and viscosity characteristics. When choosing engine oil, always refer to the grade specified in your vehicle's manual. Older vehicles might consider slightly higher viscosity oils like 40, while newer cars typically do fine with 30. Never compromise by using mismatched grades just to save money.
I used to frequently help car owners choose engine oil at the repair shop, and the model numbering rules are actually quite straightforward. Take SAE 5W-40 as an example: SAE is the international standard, the starting number 5 indicates low-temperature pumpability—the smaller the number, the smoother the cold start; the W in the middle stands for Winter suitability; the ending number 40 is the kinematic viscosity value at 100°C. Higher viscosity oils are suitable for high-temperature conditions and older engines, while lower viscosity oils save fuel but have poorer sealing performance. There are also European standards like ACEA A3/B4, which represent the oil's shear resistance. When buying engine oil, don't just look at the brand; match the certification model to your maintenance manual. German cars often require the VW502 standard.
