Modern lubricants are derived from refined petroleum. Oil manufacturers add special additives to them, which make up to 20% of engine oil. These additives, in particular, protect the oil from oxidation and prevent it from foaming at high speeds.
One of the indicators of viscosity-temperature characteristics is the viscosity index VI - this is an empirical, dimensionless indicator for assessing the dependence of oil viscosity on temperature. The higher the viscosity index value, the less the viscosity of the oil depends on temperature. An oil with a high viscosity index has better fluidity at low temperatures and a higher viscosity at engine operating temperature.
Engine oil life is affected by factors such as the amount of water, the quality of the fuel, and the presence of combustion products. Therefore, regular oil changes are necessary.
Synthetic motor oil is in most cases more expensive than mineral oil. But the high price is offset by a decrease in oil and fuel consumption, an increase in the oil change period.
Engine oil and its classification
Viscosity is the resistance to flow of a fluid. In the winter period of operation of the car, low-viscosity engine oils should be used, which provide easy start-up of the engine. In the summer period of operation, it is preferable to use more viscous oils.
SAE system (Society of Automotive Engineers of the United States). The oil designation indicates two degrees of viscosity: winter - with the letter «W» and summer - without a letter designation, for example SAE 5W-30. The lower the first number, the better the fluidity of the oil at low temperatures. The larger the second number, the higher the oil's resistance to high temperatures.
ACEA system (Nonprofit Association of Automotive Engineers). The system has been operating since 1996, replacing the SSMS system. Class A applies to gasoline engines, class B applies to diesel engines.
SSMS system (Union of Mechanical Engineers of the European Union). The oil designation consists of the letter «G» (Gas engine) or «D» (diesel engine), as well as one number. For example, CCMS G4. The higher the number, the better the quality of the engine oil.
API system (American Petroleum Institut). There are two letters in the oil designation, the first of which is «S» (Gas engine) or «WITH» (diesel engine). For example, API-SA or API-CA. The closer to the end of the alphabet the second letter, the higher the quality of the oil.
Engine oil selection
Mercedes accepts the standards of the Union of Machine Builders of the European Union (SSMS) and recommends the following oils for its gasoline engines: CCMC-G4, CCMC-G5, API-SG, ACEA A2-96 or ACEA A3-96.
API or ACEA oils are used only if CCMC oils are not available.
In the European part with a large range of summer and winter temperatures throughout the year, an oil of viscosity grade 15 W-40 or 10 W-40 can be used. Only at very low or high temperatures, which persist for a long time, should an oil of a different viscosity brand be used, consult a specialist for advice.