What Does the "W" in Motor Oil Actually Mean?

The numbers on a motor oil label represent its viscosity, and the "W" stands for Winter. It doesn’t mean weight or weather. The "W" tells you how the oil flows at low temperatures, such as when starting your engine on a cold morning.

The Society of Automotive Engineers (SAE) developed a standardized grading system to classify motor oils based on viscosity, which measures how easily oil flows at various temperatures.

Because oil naturally becomes thicker in the cold and thinner when hot, multi-grade oils were created to protect engines across a wide temperature range.

In multi-grade oils, the number before the "W" indicates how thin the oil remains in cold weather. The lower the number, the thinner and more fluid the oil is, allowing it to flow easily through the engine during startup and reduce wear when the engine is most vulnerable.

Multi-grade motor oil is formulated to respond automatically to temperature changes. Its viscosity decreases in cold weather, allowing it to flow more easily during startup, and increases in hot conditions, ensuring it stays thick enough to protect engine components under high heat.

This flexibility is essential for keeping your engine running smoothly all year. Without it, oil could become too thick in the cold, making it hard for the engine to turn over, or too thin in the heat, reducing its ability to protect moving parts. Either situation can lead to increased wear, reduced performance, or even engine failure.

Thanks to these advanced additives, multi-grade oils deliver consistent, reliable protection—whether you're starting your vehicle on a freezing winter morning or driving on a hot summer day.

Here's how 0W, 5W, and 10W oils compare:

• 0W: Best for extremely cold climates, this oil flows fast, providing quick lubrication to prevent wear during cold starts.
• 5W: Great for moderately cold weather, 5W performs well but isn’t as fast-flowing as 0W in deep freezes.
• 10W: Suitable for mild winters, 10W is thicker and slower to circulate, offering protection but with a delayed flow in colder temps.

✅ Tip: Always consult your owner’s manual to choose the right oil for your vehicle.