What does 5W-40 oil stand for?

5W-40 is a viscosity grade designation for engine oil. The "5W" indicates low-temperature fluidity, where the number 5 signifies the oil can maintain good fluidity even in extremely cold environments of -35℃, ensuring rapid engine lubrication during cold starts. "W" stands for Winter, highlighting its low-temperature performance. The "40" denotes the oil's kinematic viscosity at 100℃; a higher value indicates greater high-temperature oil film strength, effectively reducing engine component wear under high-temperature conditions. This oil is particularly suitable for turbocharged engines, high-mileage vehicles, and models frequently subjected to heavy loads or long-distance driving. Replacement is recommended every 8,000 to 10,000 kilometres or annually. When selecting oil, always check for API or ACEA certifications and avoid mixing different brands or viscosity grades to maintain optimal performance.