The tasks of engine oil
According to the operating conditions, engine oils must meet changing requirements. Therefore, it is very difficult to accurately determine the effect of various operating conditions on the lubricant. In engines that run for a long time at high speeds or at full load, high oil temperatures are reached. When exposed to high temperatures and oxidizing components of the air, oil oxidation begins. Oxidation products compact the oil and can be deposited as a varnish-like coating on the outer parts of the pistons, in the grooves for the piston rings and on the valve stems. This can lead to coking of the valve heads.
If the cylinders receive a rich mixture, the engine is rarely or almost never required high power or runs with a cool engine (city traffic), the result is imperfect combustion. Soot, oil deposits and other products, unburned fuel and moisture condensation themselves lead to the formation of deposits, acids and resins. Unburned fuel settles on the cold walls of the cylinders 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. Because when driving hard (hot engine) particles of gasoline in the oil evaporate, then. 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 refers to the fluidity of an oil. Depending on the temperature, each oil has a tendency to reduce its fluidity. As the temperature rises, it becomes more liquid. This has a negative effect on the adhesion and strength of the lubricating film. With decreasing temperature, it becomes thicker and less fluid, and the fluidity becomes more sluggish and the internal friction resistance increases. This property requires the use of engine oils with a fluidity that changes as little as possible with temperature.
When the engine is cold, it must be sufficiently fluid so that it does not impede the operation of the starter too much and so that it can reach all lubrication points as quickly as possible from the beginning of the start.
Viscosity or fluidity have the same meaning in terms of internal oil friction and are designated according to the SAE system (Society of Automotive Engineers) designations such as SAE30, SAE10, etc. High SAE numbers indicate thick oils, low SAE numbers indicate thin oils. Viscosity does not answer the question of the lubricating properties of oils.
Multigrade oils
For engines "Mercedes" both seasonal and multigrade oils can be used. All-season oils have the advantage that they are 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 the hot state, so that the required lubricity is obtained in each state. If a multigrade oil is used, stick to modern oils that have a high viscosity range (e.g. 15W-40, 15W-50).
The letter W indicates that the oil is suitable for winter.
Light oils
Light oils are multigrade oils to which additives are added to reduce the coefficient of friction, among others, so that fuel savings of up to 2% can be achieved. Light oils have a low viscosity (e.g. 10W-30). They require unusual oils in the base (synthetic oils). When buying light oils, you need to pay attention that they are suitable for "Mercedes".
Area of use (weight classes)
1. For continuous air temperatures above 30°C, SAE40 may be used.
2. Oil SAE 5W-20, applicable only at long-term air temperatures below + 10'C, SAE 10W-30 applicable in temperate climates throughout the year.
3. Oil for year-round operation.
Since the areas of application of neighboring SAE classes overlap, short-term temperature fluctuations can be ignored. It is allowed to mix oils of different viscosity grades with each other when it is necessary to add oil and the ambient temperature is not more than corresponding to the viscosity grade of the oil in the engine.
The added oil - of any kind - must not be mixed with either the fuel or the lubricating oil.
Engine oil specification
In principle, only HD oil is allowed for modern engines. HD oil is an alloy oil whose lubricating properties have been greatly improved by the addition of various chemicals. These additives contribute to better protection against corrosion, better resistance to oxidation phenomena, in particular a low tendency to form slags in the crankcase, better fluidity, cleaning and dissolving properties. Cleaning and solvent additives not only prevent the formation of deposits in the engine, but also have the ability to dissolve and distribute deposits and all other contaminants in the engine oil and keep them constantly in suspension, so that when the oil is changed, the contaminants are drained.
The quality of HD oils is indicated through the API system (API — America Petroleum Institut). European manufacturers are also guided by this system.
The designation is carried out using two letters. The first letter indicates the field of application: S - Service, for gasoline engines: C - Commerical, for diesel engines. The second letter means quality in alphabetical order.
API oils are of the highest quality: SG for gasoline engines and CD for diesel engines.
Attention: CD engine oils, which are designated by manufacturers specifically as oils for diesel engines, are not suitable for gasoline engines.
for both petrol and diesel engines. In this case, both specifications are applied on the packaging (e.g. 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, you need to pay attention to the fact that the oils used are approved for use on engines "Mercedes".
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 through leaks in the oil sump, cylinder head cover, etc.
Normal oil consumption is due to the combustion in each case of a small amount in the cylinder; due to the removal of combustion residues and wear particles. In this case, the oil is consumed due to the high temperatures and high pressures to which the engine is constantly exposed.
Further, external factors, driving style, technological deviations also affect oil consumption. In the normal case, this consumption is so small that a small addition of oil is necessary between oil changes (topping up).
It is necessary to add oil when the marking "add" reached (additive amount max. 1.5 l).