What do the letters on lubricants mean?
The mission of a lubricant is to create a protective layer for engine parts subject to friction. This prevents wear and prolongs the useful life of an automobile.
There is a letter for every type of lubricant.
The viscosity of the oil is very important and is affected by temperature. Therefore, the first letters that you must know are SAE, the initials of the Society of Automotive Engineers. This society is responsible for establishing a classification system based solely on oil viscosity. To classify the oils, their viscosity is measured in cold conditions at different temperatures below zero, and then in hot conditions at 100ºC. Taking this as the base, there are monograde and multigrade oils.
Monograde oils are suitable for specific temperatures.
What does it mean to use a monograde oil? Changing the oil during the seasons with the most extreme temperatures (summer and winter). In summer, you need a more viscous oil because the heat makes it more liquid. In contrast, in winter, you need a less viscous oil to make cold starts easier.
So, in this type of oils, the letter W, accompanied by a number, follows the SAE. This W refers to winter, and the number indicates the viscosity of the oil at low temperatures. An oil with a low SAE W number will flow better, giving easier cold starting, and reduce engine wear.
However, if instead of a W you only see numbers between 20 and 60, this refers to the oil’s viscosity at hotter temperatures. The higher the SAE grade the greater the viscosity, which translates into a thicker lubricating film and, in theory, better protection for the contact between the moving mechanical parts.
However, high viscosity when hot does not mean that the vehicle is better lubricated, since, on the contrary, excessive viscosity causes more internal friction and poorer engine performance.
Multigrade oils are suitable for a wide range of temperature.
They comply with two SAE grades and can be used at a wide range of temperatures, whether high or low. Therefore, on this type of lubricant, there are two numbers separated by a hyphen. One of the numbers is followed by a W, indicating the viscosity grade in cold temperatures. These oils do not need to be changed according to the seasons, since they are not affected by temperature in the same way as monograde oils. The viscosity grade when cold is determined by the number that precedes the W and the grade when hot is shown with no additional letter.
As a general rule, you need to follow the instructions given by the engine manufacturer, which determine the most appropriate viscosity grade for lubricating that engine. The choice depends on the engine design, weather conditions, and what the vehicle is used for.