Labels like W40-20 on engine oils refer to the oil’s viscosity rating, which indicates how thick or thin the oil is at different temperatures. Here’s a breakdown of what these numbers mean:

• “W” stands for winter, indicating the oil’s viscosity in cold temperatures.
• The number before “W” (e.g., 20 in 20W) represents the oil’s viscosity at low temperatures. Lower numbers mean the oil is thinner and flows more easily in cold conditions, which is important for starting the engine in cold weather.
• The number after “W” (e.g., 40 in W40) indicates the oil’s viscosity at high temperatures. Higher numbers mean the oil is thicker and can maintain better lubrication and protection at higher temperatures.

So, 20W-40 oil means it has a viscosity rating of 20 in cold temperatures and 40 in hot temperatures. This type of oil is designed to provide good performance in a wide range of temperatures, ensuring that your engine is protected and runs smoothly regardless of the weather.