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6.2.3. Engine oil

Engine oil prevents dry friction and wear of pistons, cylinders, bearings of a bent shaft and the valvate mechanism, in addition condenses a gap between the piston and walls of the cylinder. It undertakes functions of a cooler, taking away heat from internal walls and details of the engine. Besides, oil protects the engine from corrosion, keeps working off particles in suspension and connects a part of chemical products of combustion.
Modern lubricants receive from the refined oil. Producers of oils add to them special additives which make up to 20% of engine oil. These additives, in particular, protect oil from oxidation and prevent its foaming on high turns.
One of indicators of viscous and temperature characteristics is the index of viscosity VI is an empirical, dimensionless indicator for assessment of dependence of viscosity of oil on temperature. The value of an index of viscosity is higher, the less viscosity of oil depends on temperature. Oil with a high index of viscosity has the best fluidity at low temperatures and higher viscosity at a working temperature of the engine.
Service life of engine oil is influenced by such factors as an amount of water, quality of fuel and existence of products of burning. Therefore regular change of oil is necessary.
Synthetic engine oil is in most cases more expensive than mineral. But high price is compensated by decrease in a consumption of oil and fuel, increase in term of replacement of oil.

Engine oil and its classification
Viscosity is the resistance to a current of liquid. During the winter period of operation of the car it is necessary to apply low-viscous engine oils which provide easy launch of the engine. During the summer period of operation it is preferable to apply more viscous oils.
SAE system (Society of automobile engineers of the USA). Two degrees of viscosity are specified in designation of oil: winter — with the letter "W" and summer — without alphabetic reference, for example SAE 5W-30. The less first, the is better oil fluidity at low temperatures. The more the second, the is higher resistance of oil to high temperatures.
ACEA system (Noncommercial association of automobile engineers). The system works since 1996, having replaced the SSMS system. The class A, for diesel — a class B is applied to petrol engines.
SSMS system (Union of mechanicians of the European Union). Designation of oil consists of the letter "G" (the petrol engine) or "D" (the diesel engine), and also one number. For example, CCMC G4. The number is higher, the quality of engine oil is better.
American Petroleum Institut. In oil designation — two letters, first of which "S" (the petrol engine) or "With" (the diesel engine). For example, API-SA or API-CA. The closer to the end to the alphabet the second letter, the is higher quality of oil.

   The choice of oil for the engine
Mercedes accepts norms of the Union of mechanicians of the European Union (SSMS) and for the petrol engines recommends the following oils: CCMC-G4, CCMC-G5, API-SG, ACEA A2-96 or ACEA A3-96.
Oils on classification of API or ASEA are used only if SSMS oils are unavailable.
In the European part with a big range of summer and winter temperatures during the whole year it is possible to use oil of a class of viscosity 15 W-40 or 10 W-40. Only at very low or high temperatures remaining a long time it is necessary to use oil of other brand of viscosity, for council address experts.