Viscosity is one of the single most important characteristics of an engine oil.
Castrol®’s high-quality base oils and premium additives result in oils with a high viscosity index, which is the measure of an oil’s change in viscosity based on changes in operating temperatures.
By definition, viscosity is the measure of a lubricant’s resistance to flow. And in fact, flow characteristics and temperature are directly related. The higher the temperature, the more freely an oil flows; the lower the temperature, the more an oil’s flow is inhibited. This relationship can result in oil thinning as temperature increases and oil thickening as temperature decreases.
Oils with a high viscosity index are more resistant to excessive thinning at high temperatures and thickening at low temperatures, and, as a result, offer a wider operating range.