What does 15w40 engine oil mean?
2 Answers
The number 15 represents the minimum applicable temperature of the engine oil, which is -20 degrees Celsius. The W stands for Winter, and 40 indicates the high-temperature viscosity of the oil. This is the meaning of 15w40 engine oil. The oil grade typically represents viscosity and quality. The oil grade consists of two parts: classification and viscosity specification, with the specific interpretation as follows: The number before the W represents cold-start performance. The smaller the number, the easier it is to start the engine in cold weather. Common grades include 0w, 5w, 10w, and 15w. The number 40 indicates the viscosity characteristics of the oil at high temperatures. High-viscosity oils (with higher values) may be more suitable for high-speed driving or heavy-duty vehicles. The number after the W is an indicator of the oil's resistance to high temperatures. The larger the number, the better the oil's protective performance at high temperatures. The grade after the oil classification indicates its viscosity specification. For example, in "15w-40" or "5w-40," the lower the number before the W, the better the engine protection during cold starts. For instance, 5w can withstand external temperatures as low as -30 degrees Celsius, while 20w can withstand -15 degrees Celsius. The number after the W represents the oil's kinematic viscosity at 100 degrees Celsius. The higher the number, the higher the viscosity. The viscosity of lubricating oils is often labeled using SAE grades. SAE is the abbreviation for the "Society of Automotive Engineers" in English. Internationally, the SAE (Society of Automotive Engineers) viscosity grades and API (American Petroleum Institute) quality grades are widely adopted. When selecting engine oil, consider the following precautions: Choose engine oil based on the engine's requirements. There is no need to use overly advanced oil in engines with lower requirements, nor should lower-grade oil be used in engines with higher requirements. It is advisable to choose multi-grade oil whenever possible. Multi-grade oil is economical, long-lasting, and efficient, providing better protection for the engine. Due to the characteristics of multi-grade oil, it may appear darker prematurely, and the oil pressure may be lower than that of conventional oil during use. These are normal phenomena. Never mix different grades of engine oil, as this can damage internal engine components and shorten the maintenance interval.
I understand that 15W-40 oil refers to an SAE viscosity grade lubricant. The number 15W indicates its flowability at low winter temperatures, where 15 represents the viscosity index—the lower the number, the easier cold starts are, and W stands for Winter. The 40 denotes the viscosity at high temperatures of 100°C, with higher numbers indicating thicker oil that better protects the engine from high-temperature wear. This type of oil is particularly suitable for diesel vehicles, older high-mileage cars, or models frequently driven in tropical high-temperature regions, as it maintains stability across varying temperatures to ensure steady oil pressure. However, I recommend checking the owner's manual when selecting oil, as incorrect viscosity may increase fuel consumption or accelerate engine component wear. Remember, regular oil changes are also crucial—replacing it every 5,000 to 7,500 kilometers can extend engine life.
