Whats the difference between a multigrade and a monograde?
The main difference between these two types of engine oil is their fluidity at cold start.  Multigrades, such as 10W/40, 15W/40, 5W/30, etc., flow more easily and are therefore pumped round to the critical components much more quickly. Historically, the ‘W’ stands for winter. As well as this important feature, multigrades also have to provide a protective oil film at higher temperatures when the engine has warmed up.  Monogrades on the other hand provide a very good oil film at working temperatures, but their cold start properties are poor. To overcome this it used to be the practice to put a thin monograde, such as a SAE 30, in the engine during the winter and a heavier monograde, such as a SAE 50.
