Answer to Question #340290 in General Chemistry for denden

Question

The society of Automotive Engineers rates the viscosity of motor oils. Some typical ratings are SAE 40 and SAE 15, where the number is the measure of the relative viscosity. Higher numbers are given to oils that are more viscous. Oils suitable for use during winter have a W placed after the number in the viscosity rating. Which of these oils (SAE 40 or SAE 15) could be used during the winter and this have a W in the rating. Explain

Answer 1

With increasing temperature, the viscosity of oils falls quite rapidly. In some cases the viscosity of oil can fall by about 80% with a temperature increase of 25°C. From the engineering viewpoint it is important to know the viscosity value at the operating temperature, because it determines the lubricant film thickness separating two surfaces. The oil viscosity at a specific temperature can be either calculated from the viscosity-temperature equation or obtained from the viscosity-temperature ASTM chart.

. Winter engine oil, in contrast to the summer counterpart, should be more fluid for better engine start to "cold".

So for winter we should choose oil with lower viscosity SAE15