What does 5W-40 mean?

The term 5W-40 refers to the viscosity grade of engine oil, as specified by the Society of Automotive Engineers (SAE). The "5W" indicates the oil's viscosity at low temperatures (the 'W' stands for winter), meaning it flows well in cold conditions. The "40" denotes the oil's viscosity at high temperatures, ensuring it remains thick enough to protect engine components under heat. This designation helps ensure that the oil performs effectively across a range of temperatures.