What does 15w40 engine oil mean?

[JosephineMarie]

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.

[Phil]

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.

[DelDawson]

I often use automotive-related experience to explain the meaning of 15W-40 oil. Simply put, it is a multi-grade oil. The 15W part refers to its performance in low-temperature environments—the lower the value, the easier it is to start the engine smoothly in cold weather. The 40 indicates high-temperature viscosity, ensuring the oil doesn’t thin out excessively in hot conditions, providing reliable lubrication. This makes it widely used in SUVs, trucks, or scenarios involving prolonged high-load driving. When choosing oil, seasonal changes should be considered. 15W-40 is practical in temperate regions, and if your car is often used for urban commuting, it is both fuel-efficient and durable. However, excessive use of high-viscosity oil in winter may increase starting difficulties. Always check if the oil grade meets your vehicle’s standards to protect the powertrain.

[LaCharlie]

I think 15W-40 oil means it performs well in both cold and hot temperatures. The 15W indicates cold-start performance, with a lower number like 15 making winter starts easier; the 40 represents high-temperature viscosity, suitable for hot weather. This type of oil is commonly used in diesel engines or commercial vehicles, such as trailers or construction site vehicles, because it prevents part wear under heavy loads. If your car is driven in high-temperature southern regions, it's a good choice; in northern winters, switching to 5W-30 might make cold starts easier. Using the wrong oil can damage the engine, so always refer to the manual for the correct specification when changing oil.

[McAndrew]

I emphasize that 15W-40 oil is a multi-grade viscosity, where 15W aids in cold-weather flow to reduce startup wear, while 40 ensures high-temperature protection. This type of oil performs exceptionally well in high-temperature environments, such as during summer long-distance driving or frequent heavy-load situations, maintaining stable oil pressure to prevent overheating. Using the wrong oil can lead to wasted fuel and increased noise. I recommend selecting oil based on actual driving conditions and adhering to regular changes every 6 months or 7,000 kilometers to keep the engine running smoothly.