What does 5w-40 engine oil mean?

[Galadriel]

5w-40 engine oil means: 5 represents the fluidity of the oil, the smaller the number, the better the fluidity of the oil, and it also indicates the minimum temperature value that the oil can be applied to; w is the abbreviation of Winter; 40 represents the viscosity of the oil, the larger the number, the greater the viscosity of the oil, the better the high-temperature protection performance, and the greater the corresponding resistance. 5w-40 engine oil is suitable for electronically injected gasoline engines with crankcase ventilation devices and catalytic converters, as well as turbocharged intercooled direct-injection diesel engines with crankcase ventilation and exhaust gas recirculation devices, operating under various working conditions. Such engines usually operate under extreme temperatures and may have longer oil change intervals, which can put great pressure on the engine, leading to reduced engine sensitivity and performance degradation. The oil contains top-level power cleaning and dispersing technology, which, compared with traditional lubricating oil, can persistently prevent the formation of sludge and carbon deposits, effectively protect the engine, and significantly improve vehicle performance.

[AutumnMarie]

I often help friends choose motor oil, so 5W-40 oil is a specification under the SAE viscosity standard, which refers to the fluidity changes of oil at different temperatures. The 5W represents low-temperature viscosity, where the number 5 indicates that the oil is thin and flows well during cold winter starts, quickly lubricating engine components to prevent cold-start wear; the W stands for winter. The 40 denotes high-temperature viscosity, meaning that when the engine heats up during operation, the oil maintains a viscosity level of 40, providing sufficient thickness to isolate high-temperature friction. This type of oil is designed for flexibility, suitable for year-round driving, especially in all-weather regions like northern China, where winters are cold and summers are hot, balancing protection and fuel economy. Remember not to use the wrong viscosity—always check your vehicle's manual for recommendations, as choosing incorrectly may harm the engine or increase pollution. Regular oil changes every 5,000 kilometers are also crucial.

[CorbinDella]

As a daily commuter, I understand that 5W-40 oil refers to the viscosity grade of the lubricant. The 5W part indicates the oil becomes thinner at low temperatures for easier flow, while the 40 part means it thickens when the engine is hot to prevent high-temperature wear. Combined, it represents a multi-grade oil that automatically adjusts to both cold and hot conditions. I recommend prioritizing the vehicle manufacturer's specifications – for instance, Volkswagen models commonly use this grade. Benefits include reduced engine noise and improved fuel economy. Replacement intervals vary by usage; for urban short-distance driving, changing every six months is more prudent. Always avoid substandard oils and purchase reputable brands for safety.

[StFelix]

I've studied the principles of motor oil. Simply put, 5W-40 refers to viscosity grading. The number 5 indicates strong low-temperature fluidity, enabling smooth engine starts below -20°C; the W stands for winter suitability; and the number 40 ensures stable protective layers at high temperatures of 100°C. This design allows the oil to maintain efficiency during temperature fluctuations and reduces piston wear. I compared it with single-grade oil—the latter lacks versatility, while 5W-40 is more all-round. Regular oil changes prevent carbon buildup.