4.9.8 Oil used for lubrication
Oils of mineral (now rare), semi-synthetic and synthetic origin are used for the lubrication of engines.
Special additives (special chemical compounds) are added to oil in order to improve its quality. These additives increase the lubricity of the oil, make its viscosity more stable, lower the pour point, reduce the oxidizing effect of oil. Additives in the oil also help washing away resinous deposits from the gaps of rubbing parts, etc.
Depending on the season and climatic conditions, oils of different viscosities should be used for lubricating the engine. In winter, the viscosity should be less, because oil with a high viscosity at low temperatures will thicken and in a cold engine it will not penetrate well into the gaps of rubbing parts. It will also be difficult to fill in oil and start a cold engine.
In summer, the viscosity of the oil should be higher, because oil with a low viscosity at elevated temperatures becomes even more liquid and does not provide normal engine lubrication. However, all-season engine oils are commonly used nowadays.
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