Seasonal or multigrade oil?
In order for the starter to be able to crank a cold engine, the oil must not offer too much resistance. In addition, it must reach all those places where lubrication is needed as quickly as possible; for this it must be fluid. On the contrary, at high temperatures and speeds, the oil must be sufficiently viscous so that the lubricant film does not break. Unfortunately, mineral oil has the opposite effect. When cold, it is viscous, as it warms up, on the contrary, it is fluid. Therefore, it is necessary that the oil and the prevailing operating temperatures of the engine correspond exactly to each other.
The nature of the fluidity, i.e. viscosity or fluidity, given by the viscosity grade of the oil. The corresponding classes have been defined by the American Association of Automotive Engineers (Society of Automotive Engineers) (SAE). Motor oil viscosity grades range from SAE 5 W, 10 W winter oils to SAE 20W/20 intermediate grade and then to SAE 30, 40 and 50 summer oils.
- Seasonal oil used to be the cheapest. To ensure perfect lubrication of the engine, it must be viscous or fluid according to the season. Today, seasonal oil is almost never found in gas stations or supermarkets, but is still often used in the truck fleet.
- All-weather oil is much more expensive to manufacture, so its price is higher. It has an improved viscosity index (VI) long chains of molecules that swell when heated and shrink again when cooled. In this regard, the oil can plastically adapt to temperature and, according to its characteristics, cover several viscosity classes. Oil SAE 15 W-50 at a temperature of -15°C corresponds to a viscosity class of 15 W and at 100°C to a class of 50.
A problem with multigrade mineral oils is that the molecular chains of their viscosity additives can shear off over time. In this case, the upper viscosity class is not completely preserved, the oil is no longer so resistant to temperature.
Oil of the right viscosity
At what temperatures, what viscosity is required for the Vectra engine oil, shown in the graph on the previous page. The table shows that Opel also allows seasonal oil. This is a savings opportunity if you do not subject your car to a continuous load at the limit of power. Seasonal oils are just as good as multigrade oils, but they can cover narrower temperature ranges. In any case, in the cold season with its strong temperature fluctuations, all-weather oils seem to be preferable to us.
With high performance oils, the temperature problem is no longer a problem (see next. chapter).
High performance oils
- Lubricating oils that are very thin when cold, especially during the warm-up phase and when driving over short distances, significantly reduce the internal friction in the engine, i.e. give him less resistance. You can realistically count on a reduction in gasoline consumption by about 3%. But these savings cannot be taken into account in engines with high oil consumption.
- Partially and fully synthetic oils are generally among the most expensive oils. They consist (partially) from artificial chemical compounds of elements such as carbon, hydrogen and oxygen. In this case, only those molecules were selected that were able to optimally perform the required lubrication tasks. In practice, this means that these oils, unlike mineral oils, age much more slowly. They also evaporate less quickly and are permanently shear stable, i.e. they retain their original highest viscosity grade for a long time.
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