Oil viscosity
Viscosity of motor oils
Viscosity characterizes the fluidity of an oil. Depending on the temperature, the oil tends to decrease in fluidity. As the temperature increases, the oil becomes more fluid. This impairs the oil's ability to adhere and resist high contact pressures. As the oil cools, it thickens, fluidity decreases, and internal friction increases. Because of this property, it is necessary to use an engine oil with a viscosity that changes as little as possible with temperature changes.
When starting a cold engine, the oil must be thin enough so that it does not overload the engine excessively and so that after starting, the oil will quickly penetrate into all places where lubrication is needed.
Oil fluidity is equivalent to its internal friction and is indicated by SAE units (Society of Automotive Engineers - Association of Automotive Engineers), for example SAE 30, SAE 10. A high SAE indicates that the oil is thick, a low SAE indicates a thin oil. However, the viscosity of the oil does not fully characterize the lubricating properties of the oil.
Multigrade oils
In car engines, it is preferable to use multigrade oils. The advantage of all-season oils is that they do not need to be selected depending on the time of year. They are made on the basis of liquid one-season oil (type 10W). When heated, this oil is stabilized by a so-called thickener, which ensures the appropriate lubricating properties of the oil at all temperatures. When using all-weather oil, modern grades with a wide temperature viscosity range should be used, for example 10W-40, 15W-50.
Letter W (winter - winter) in the SAE designation, it characterizes the suitability of the use of oil in the winter.
Viscosity grades and range of oil use
Since the range of use of neighboring SAE classes overlaps, short-term temperature fluctuations can be ignored. Mixing oils of different viscosity grades is allowed if topping up of oil is required, and the ambient temperature no longer corresponds to the viscosity grade of the oil filled into the engine.
At long outside temperatures below -20°C, it is recommended to fill in SAE 5W-20 oil.
Warning: CD engine oils, which are designated by the manufacturer as diesel engine oils, are not suitable for gasoline engines. There are oils that can be used in two types of engines, in which case both designations are indicated on the oil container, for example SG / CD.
Warning: Additional oil additives, regardless of their type and purpose, should not be added to the oil.
Engine oils
For modern engines, only D oils should be used. HD oils are oils with increased lubricity properties, improved by various additives. These additives provide better anti-corrosion protection, more favorable conditions against oxidation phenomena, the least tendency to form slags, the best viscosity change, cleaning and dissolving properties. Cleaning and dissolving additives not only reduce the formation of residues in the engine, but at the same time they have the ability to dissolve and hold these residues and all other contaminants in the engine oil in a suspended state so that when the oil is changed, these contaminants are removed along with the drained oil.
The quality of HD oils is determined by the API system (American Petroleum Institut). European manufacturers also follow this system.
The designation of the oil grade is made in two letters. The first letter characterizes the scope: S - Servise, designed for carburetor engines; C - Commercial, designed for diesel engines.
The second letter identifies the grade of oil in alphabetical order.
API premium oils are SG for carbureted engines and CD for diesel engines.
Gasoline engines
- A - all-weather oils with increased anti-friction properties, specification VW 500 00.
- B - all-weather oils, specification VW 501 01;
- multigrade oils, API-SF or SG specifications.
Diesel engines
- A - all-weather oils with enhanced anti-friction properties, specification VW 500 00 (for turbocharged diesel engines only in mixtures with specification VW 505 00).
- B - multigrade oils, specification VW 505 00 (unlimited for all diesel engines);
- multigrade oils, API-CD specification (for turbocharged diesel engines only in case of emergency for topping up);
- multigrade oils, specification VW 501 01 (for turbocharged diesel engines only in mixtures with specification VW 505 00).
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