What is meant by multigrade?

Multigrade oils

These were developed in the 1960’s and have many different viscosities (20W50, 20W60 etc.).  Prior to this, all oils were monogrades (ie. 30, 40, 50).

This development was made possible by the invention of polymers.   Polymers are molecules that expand as they get hotter.  Therefore a multigrade oil can have the viscosity of an SAE 20 when it is cold and the viscosity of an SAE 50 when hot.  This removes the necessity to change from a thin oil in the winter to a thicker oil in the summer.

The 20w number is the cold viscosity and the 50 number is the viscosity at 100 degrees centigrade.

For details on all of engine oils produced by Millers Oils, please see our full range of Classic Engine Oils, Motorsport Engine Oils and Road Car Engine Oils.

For other useful info please refer to our FAQs page.