What do the numbers tell you about the area of application for a particular oil?
Multigrade oils feature 2 numbers in the SAE grading specifications (SAE: Society of Automotive Engineers) , e.g. 0W-40.
These indicate to which warmth and coldness ranges the engine oil is best suited. The letter ‘W’, means winter and how viscous (or fluid) the oil remains in cold weather - the lower the number, the better the viscosity of the oil. Therefore, 0 signifies an extremely viscous oil that can be used at low temperatures.
The second part of the details on viscosity (the number after ‘W’) indicates how viscous the oil is at high temperatures - the higher the number, the thicker the film of oil will be.
So 10 would stand for a very viscous oil that has specially been conceived for cold environments. Number 60 is to be used in extremely hot locations and is extremely thick in its normal state. 40 would therefore correspond to average viscosity and would guarantee optimal use even at high temperatures.