Contents: The tasks of motor oil ↡ Viscosity of motor oils ↡ All-season oils ↡ Light oils ↡ Area of use (classes of carrying…↡ Specification of motor oils ↡ Oil consumption ↡
The tasks of motor oil
According to the operating conditions, engine oils must meet changing requirements. Therefore, it is very difficult to accurately determine the effect of different operating conditions on the lubricant. In engines that operate for a long time at high speed or at full load, high oil temperatures are reached. When exposed to high temperatures and oxidizing components of the air, oxidation of the oil begins. Oxidation products thicken the oil and can be deposited as a varnish-like coating on the outer parts of the pistons, in the piston ring grooves and on the valve stems. This can lead to coking of the valve plates.
If the cylinders receive an over-rich working mixture, high power is rarely or almost never required from the engine, or the engine is driven with a cooled engine (city traffic), then the consequence of this is imperfect combustion. Soot, oil carbon and other products, unburned fuel itself and condensation of moisture lead to the formation of sediments, acids and resins. Unburned fuel settles on the cold cylinder walls and flows down into the crankcase, washing away the oil film from the pistons and cylinders. The consequence is reduced lubrication of the pistons and dilution of the oil, which has a negative effect on the lubricating properties of the oil due to the presence of fuel in it.
If the oil is heavily diluted, it is necessary, depending on the circumstances, to carry out an early oil change. Since with intensive driving (hot engine) gasoline particles in oil evaporate, especially in winter (many cold starts, high gasoline content in oil), you need to check the condition of the oil more often.
Viscosity of motor oils
Viscosity is the fluidity of oil. Depending on the temperature, each oil has a tendency to decrease its fluidity. As the temperature increases, it becomes more liquid. This has a negative effect on the adhesive ability and strength of the lubricating film. As the temperature decreases, it becomes thicker and less fluid, and the fluidity becomes more sluggish and the internal friction resistance increases. This property requires the use of motor oils with a fluidity that changes as little as possible with temperature.
When the engine is cold, it must be fluid enough so as not to impede the starter's operation too much and so that it can reach all lubrication points as quickly as possible from the start.
Viscosity or fluidity have the same meaning in terms of internal friction of oil and are designated in accordance with the SAE system (Society of Automotive Engineers) such designations as, for example, SAE30, SAE10, etc. High SAE numbers indicate thick oils, low ones indicate thin oils. Viscosity does not answer the question about the lubricating properties of oils.
All-season oils
Both seasonal and all-season oils can be used for Mercedes engines. All-season oils have the advantage of being adapted to summer/winter temperature ratios.
All-season oils are made from liquid seasonal oils (e.g. 15W). With the help of so-called thickeners, the oil is stabilized in a hot state, so that the required lubricating ability is obtained in each state. If an all-season oil is used, it is necessary to stick to modern oils that have a high viscosity range (eg 15W-40, 15W-50).
The letter W indicates that the oil is suitable for winter.
Light oils
Light oils are all-season oils to which additives are added, among other things, to reduce the coefficient of friction, so that fuel savings of up to 2% can be achieved. Light oils have low viscosity (eg 10W-30). They require unusual oils in the base (synthetic oils). When buying light oils, you need to pay attention to whether they are suitable for Mercedes.
Area of use (classes of carrying capacity)
1. For continuous air temperatures above 30°C, SAE40 can be used.
2. SAE 5W-20 oil is applicable only at long-term air temperatures below +10°C, SAE 10W-30 is applicable in temperate climate zones throughout the year.
3. Oil for year-round use.
Since the application areas of adjacent SAE classes overlap, short-term temperature fluctuations can be ignored. It is permissible to mix oils of different viscosity classes with each other when it is necessary to add oil and the ambient air temperature is no higher than that corresponding to the viscosity class of the oil in the engine.
The added oil - of any kind - must not be mixed with either the fuel or the lubricating oil.
Specification of motor oils
In principle, only HD oil is permitted for modern engines. HD oil is an alloyed oil, the lubricating properties of which are significantly improved by adding various chemicals. These additives contribute to better corrosion protection, better resistance to oxidation, especially a low tendency to form slags in the crankcase, better fluidity, cleaning and dissolving properties. Cleaning and dissolving additives not only prevent the formation of sediment in the engine, but also have the ability to dissolve sediment and distribute it and all other contaminants in the engine oil and constantly hold it as a suspension, so that when changing the oil, the contaminants drain.
The quality of HD oils is designated by the API system (API — America Petroleum Institute). European manufacturers are also guided by this system.
The designation is made using two letters. The first letter indicates the area of application: S - Service, for petrol engines: C - Commerical, for diesel engines. The second letter indicates the quality in alphabetical order.
The highest quality oils are those according to API specification: SG - for gasoline engines and CD - for diesel engines.
Please note: CD motor oils, which are specifically designated by manufacturers as oils for diesel engines, are not suitable for petrol engines.
for both petrol and diesel engines. In this case, both specifications are printed on the packaging (eg SF/CD). For Mercedes, SF brand motor oils according to API specification are suitable. High-quality SG specification oils can also be used. In this case, it is necessary to pay attention to the fact that the oils used are approved for use in Mercedes engines.
Oil consumption
In an internal combustion engine, oil consumption is understood as the amount of oil that is consumed as a result of combustion processes. In no case should oil consumption be identified with the loss of oil that flows out through leaks in the oil pan, cylinder head cover, etc.
Normal oil consumption occurs due to the combustion of a small amount in each cylinder; due to the removal of combustion residues and wear particles. At the same time, oil is consumed due to the high temperatures and high pressures to which the engine is constantly exposed.
Furthermore, external factors, driving style, and technological deviations also affect oil consumption. In the normal case, this consumption is so small that a small addition of oil (topping up) is necessary between oil changes.
It is necessary to add oil when the "add" mark is reached (additive amount maximum 1.5 l).