What is viscosity and what is the difference between monograde and multigrade?
In order for motor oil to perform its major function – lubrication – its viscosity (in measures of its thickness or resistance to flow) must be capable of holding up under extreme temperature conditions. Oil thins when heated and thickens when cooled. A grading system like this is used: “XXW-XX”, with the first part eg. “10W” indicating the oil’s viscous characteristics at cold temperature and the second part eg. “40” indicating those at operating temperature. Oils which only display a single viscosity grade 30, 40, or 50 are known as a monograde. Monogrades must be replace seasonally (winter and summer) to ensure appropriate viscosity, therefore the majority of engine oils are multigrade.
