Oils as lubricants play an important role in the car.
Lubricants are a separating agent between two frictional elements that are in motion relative to each other. Oil prevents direct contact, minimizing friction and reducing wear. Oil as a lubricant is found in the engine, transmission and differential.
The quality of the oils depends on the refining of the base oil and the additives. Nowadays, because of the high stresses involved, partially and fully synthetic oils are often used.
They also make it possible to considerably lengthen the intervals between engine oil changes. An important classification is made on the basis of viscosity grades (SAE = Society of Automotive Engineers). The viscosity is a measure of the internal friction that resists the flow of the lubricating oil. Today, mainly multigrade oils are on the market that can be used with greater differences of ambient temperatures and thus are suitable for year-round use.
They carry identifying codes such as 10W-40. The first number gives information about the cold-running properties (eg: 10W means from -20°C). The second number quantifies the viscosity at 100°C. The higher the second number is, the better the lubricating properties at high temperatures are.