By adding the so-called «viscosity index improvers» stabilization of all-weather oils in a hot state is ensured.
In this way, the necessary lubrication of the engine is ensured both in cold and hot conditions. The SAE designation indicates the viscosity of the engine oil.
SAE - Society of Automotive Engineers (Society of Automotive Engineers)
For example, SAE 10 W 40 stands for:
10 - the viscosity of the oil in a cold state. The lower this number, the lower the viscosity of cold engine oil.
W - indicates that the oil is suitable for winter operating conditions.
40 is the viscosity of the hot oil. The higher this number, the higher the viscosity of hot engine oil (see illustration 8.0).
Lightweight oils can also be used (low friction oils). We are talking about all-weather oils, which include additives that facilitate the coefficient of friction, as a result of which there is a decrease in friction of internal engine parts.
The basis of easy-flowing oils is synthetic oil.
Illustration 8.0 shows the viscosity of engine oils as a function of ambient temperature.
Due to the fact that the fields of application of adjacent oils according to the SAE classification overlap, short temperature fluctuations can be ignored.
It is allowed to mix oils of different viscosities if it is necessary to add oil, and the air temperature does not correspond to the viscosity class of the oil poured into the engine.
Attention! Lubricating additives of any kind must not be added to fuels or lubricating oils.
Engine oil specification
The quality of engine oil is indicated by the relevant standard of vehicle and oil manufacturers.
Classification of motor oils of American manufacturers is carried out according to the API system: an abbreviation from the first letters of the American Petroleum Institute (American Petroleum Institute).
The designation is made using two letters. The first letter indicates the scope:
- S - for internal combustion engines;
- C - for diesel engines.
The second letter in the designation indicates the quality of the oil and is used in alphabetical order.
The highest quality oils are of specification SL for internal combustion engines and CF for diesel engines.
European oil manufacturers apply the ACEA specification (Association des Constructeurs Europens d'Automobiles), which specifically takes into account European engine technology.
Oils for gasoline engines of passenger cars have ACE A classes from A1-96 to AZ-96; for diesel engines -classes from B1-96 to B4-96. The highest quality oils are A3 oils for gasoline and B3 oils for diesel engines.
Oils with the designation B4 are intended only for use on engines with direct fuel injection. However, they can only be used if the B3 specification is also indicated on the packaging.
The numbers 96 indicate the start of the ACEA specification. This means that this specification was put into effect in 1996. Engine oils with earlier specifications can also be used.
Attention! Engine oils marked by the manufacturer as being for diesel engines cannot be used in gasoline engines. However, there are oils that are suitable for both gasoline and diesel engines. In such cases, both specifications are printed on the packaging of motor oils intended for both gasoline and diesel engines (e.g. ACEA A3-96/B3-96 or API SH/CF).
Recommended engine oil for A-class vehicles
Petrol engines:
- API-SG or higher;
- ACEA A3-96.
Diesel engines:
- API-CE or higher;
- ACE A B 3-96;
- ACEA A3-96/B3-96.