Archive for March 27th, 2010
Monograde and Multigrade Oils
A way to classify the motor oil is to add the letter “W” behind the number. The “W” stands for winter and indicates that an oil is suitable for use in colder temperatures. The lower the number in front of the “W”, the better the cold temperature protection. This service classification mainly looks at the low temperature viscosity of the oil.
SAE20 and SAE20w are two totally separate monograde classifications. SAE20 describes the high temperature viscosity of the oil and SAE20w describes the low temperature cranking capability of the oil.
In order to allow engines to start at low temperatures while providing sufficient viscosity at high temperatures to protect engines against wear, multigrade oils were developed. An oil can be classified as a multigrade SAE 20w-20 if the can meet both the low temperature cranking viscosity of 4500 cP at -15C and the 100C high temperature kinematic viscosity requirement between 5.6 and 9.3 cSt.