A #lubricant is a substance, usually organic, introduced to reduce #friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces..
Lubricants for internal combustion #engine contain additives to reduce oxidation and improve lubrication.
The Society of Automotive Engineers (SAE) has established a numerical code system for grading motor oils according to their viscosity characteristics
XXW YY The first number ‘XXW’ is the equivalent grade of the single grade oil that has the oil’s viscosity at cold temperature and the second number is the grade of the equivalent single-grade oil that describes its viscosity at 100 °C
For example : 10W 40 : ’10W’ is the grade of viscosity in cold and the oil is more thinness when this number is lower
’40’ is the grade of #viscosity in 100°C and it refer that the oil more thickness at high temperature when this number is higher
This code is grade not the viscosity amount .