How can I know the viscosity of a Lubricant when buying it?
The SAE organization has established an internationally accepted standard based on the differentiation of viscosity at different temperatures.
This classification defines a series of grades for engine oils and contains two sub-classifications: one designated by a “W” which refers to the properties of the oil at low temperatures, and another without “W” which refers to the properties at high temperatures.
Therefore, oils designated with a numerical grade followed by the letter W (such as SAE 10W) or simply with a number (such as SAE40) are called “monograde” oils. On the contrary, those which are designated by the two types of grade (such as SAE 10W-40) are called “multi-grade” because they are capable of simultaneously bringing together viscometrical properties at both low and high temperatures.