Seasonal or all-season oil?
In order for the starter to turn over a cold engine, the oil must not offer too much resistance. In addition, it must reach all the 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 viscous enough so that the lubricant film does not break. Unfortunately, mineral oil has the opposite properties. 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 exactly match each other.
The nature of the fluidity, i.e. viscous flowability or fluidity, is given by means of the viscosity class of the oil. The corresponding classes have been defined by the American Association of Automotive Engineers (Society of Automotive Engineers) (SAE). Viscosity grades of motor oils range from winter oils SAE 5 W, 10 W to the intermediate class SAE 20W/20 and then to summer oils SAE 30, 40 and 50.
- Seasonal oil used to be the cheapest. To ensure perfect lubrication of the engine, it must be viscous or thin-flowing according to the season. Today, seasonal oil is almost never found at petrol stations or supermarkets, but is still often used in the truck fleet.
- All-season 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. Due to this, the oil can plastically adapt to temperature and cover several viscosity classes in its characteristics. SAE 15 W-50 oil at a temperature of -15°C corresponds to viscosity class 15 W and at 100°C - class 50.
The problem with all-season mineral oils is that the chains of molecules of their viscosity additives can be cut off over time. In this case, the upper viscosity class is not fully preserved, the oil is no longer as temperature-resistant.
Oil of the required viscosity
At what temperatures and what viscosity oil is required for the Vectra engine is shown in the graph on the previous page. The table shows that Opel also allows the use of seasonal oil. This is an opportunity to save if you do not subject your car to prolonged load at the power limit. Seasonal oils are no worse than all-season oils, but they can cover narrower temperature ranges. In any case, in the cold season with its strong temperature fluctuations, all-season oils seem preferable to us.
With high-performance oils, temperature is no longer a problem (see next section).
High performance oils
- Very liquid when cold, easy-flowing lubricating oils, especially during the warm-up phase and when driving short distances, significantly reduce internal friction in the engine, i.e. they provide less resistance to it. You can realistically expect a reduction in gasoline consumption of about 3%. But this saving 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 (partly) of artificial chemical compounds of elements such as carbon, hydrogen and oxygen. 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 significantly more slowly. They also do not evaporate as quickly and have constant shear stability, i.e. they retain their original highest viscosity class for a long time.
[Article published on the website: OPELBOOK]
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