Why does honey flow more slowly than water? Because of the difference in its viscosity. Viscosity is the measure of a fluid’s resistance to flow. Water, for example, flows much faster than honey or maple syrup (if you prefer that in your morning coffee) when poured from a container. That’s because water has a lower viscosity.
Here’s the straight story on viscosity grade. The “W” number in, for example, a 15W-50 motor oil outlines the viscosity requirements of the oil when it is cold. This means that a 15W-rated oil has to meet certain criteria at cold temperatures. Taking our 50-weight example, a 15W-rated oil will flow more freely than a 20W-rated