Basic functions of an engine oil:
An engine oil is a mixture of so-called base oils and improvers. Base oils are obtained by processing petroleum and constitute a mixture of hydrocarbons of different structures and properties. In addition to base mineral oils, there are synthetic oils and mixtures of mineral and synthetic oils (so-called semi-synthetic base oils).
Improvers applied in modern high quality engine oils constitute approx. 30% of oil volume. They are intended to improve oil parameters. Important parameters such as flashpoint and evaporation rate depend on the composition and properties of a base oil. Both depends mainly on the quantity of volatile fractions in oil. Flashpoint is usually 200-240°C.
Base oils are not capable of meeting all requirements expected from an engine oil. This is achieved by enriching base oils with improvers. These include single chemical compounds or their mixtures. Improvers are intended to increase performance of base oils and protect a finished oil from changes in its properties under operation.
The amount of improvers in an engine oil depends on the oil quality grade. The higher the class of oil, the higher the content of improvers. - Viscosators – increase viscosity and oil viscosity rate. In some cases, it is possible to reduce the oil pour point.
A finished engine oil is obtained by mixing (blending) the above components.
Oil serves as a lubricating agent by creating a thin layer on the working surface, i.e. an oil film. Optimal lubrication of a single couple is under smooth friction conditions at complete separation of mating components with a continuous oil layer, i.e. a lubricating film.
Oil must have proper viscosity properties in order to effectively lubricate an engine, i.e. a component consisting of numerous moving pairs, within a wide range of temperatures, e.g. under winter conditions up to 150°C and higher at normal operation. Oil is applied to separate two surfaces moving in respect of each other, ensuring a so-called fluid friction where there is no direct contact between metal engine elements such as sliding bearings.
For this purpose, oil must be sufficiently liquid at low temperature and have suitable kinematic viscosity at high temperatures. Oil in a cold engine must get to the most distant engine elements subject to lubrication as soon as possible, therefore it should be sufficiently liquid at low temperatures and ensure proper penetration in all friction couples. In a hot engine, an oil film must not be broken, i.e. oil at high temperatures and under heavy loads must not be too ‘thin’.
Secondary gear and transmission gear boxes are another challenge for oil. An oil film must be resistant to high pressure on the surface of sprocket wheels, whereas in a wet clutch (if installed in a motorcycle) discs must stick together when the engine is still cold.
The sealing function is provided by an engine oil mainly in a cylinder – piston rings – piston system. In order to obtain continuous lubricating oil on the cylinder bearing surface through a so-called sealing ring, suitable viscosity of the oil at operating temperature (150-315°C) is necessary. The pumping effect of piston rings is also observed in this system. It results in losses of certain amounts of oil fed to the combustion chamber.
In order to ensure that the system properly fulfils the sealing function which isolates the combustion chamber from the space under the piston, it is required to allow the rings to freely move in the piston grooves. Without a thin layer of oil under the piston rings, high pressure gases in the combustion chamber would penetrate into the inside of the crankcase, causing a significant engine performance drop. Owing to the sealing function of oil around the piston walls, gases generated in the combustion process do not move from the combustion chamber to the crankcase.
Different impurities are formed in oil when the engine is under operation, which adversely affect its performance and durability. They can be divided into external and internal engine impurities due to their origin. Some impurities tend to form deposits on internal engine surfaces and this can be prevented by defining suitable properties of an engine oil.
Generally, solid particles (dust) with air, fuel and fresh oil fed to proper engine units come from the outside. The amount of such impurities depends on the purity of supply substances, a degree of their filtering at the engine inlet and on the level of technical service. Some water diluted in fuel, fresh oil and in the form of water mist in air may be transferred this way.
Internal-origin impurities include particles of dust, filings, dirt, etc., products of worn friction engine components, fuel combustion products and portions of oil blown from the combustion chamber (soot, sulphur dioxide, sulphurous acid anhydride, water) and oil oxidation products accumulated in a new or repaired engine. Oil leakage to an oil sump caused by ‘infiltration’ of injection units in diesel engines or a mixture with too many improvers in spark-ignition engines should also be mentioned. Different contaminating substances are formed in the process of oxidation, occurring particularly during lubrication when the oil is in a thin layer at increased temperature and additionally catalyst-supported by a metallic surface. In a combustion engine, oxidation takes place in the oil sump, on the cylinder bearing surface and in the bottom piston parts, whereas the process of thermal degradation and combustion of oil is predominant in the section of top piston rings.
Yes, provided that the same SAE viscosity grade and ACEA quality classifications are maintained in oils to be mixed.
It is not recommended to change a mineral oil to a synthetic or semi-synthetic one. In older-generation vehicles it may cause the engine lubrication system becoming unsealed as a result of damage to elastomers installed in the system. In high-mileage engines, a synthetic oil may cause increased oil losses during operation.
It is a normal phenomenon when operating a car with a diesel engine. The oil turns black because one of its functions is to absorb combustion process impurities, to include soot which gives a characteristic black colour.
There are two basic reasons for this: the first and the most common one is an excessive amount of soot in oil. This may be caused by an incorrectly adjusted injection unit or an obstructed air filter. Furthermore, tough operating conditions also contribute to an increased soot content in oil.
The second, much more hazardous case is contamination of an engine oil with glycol from the engine cooling system. The process occurs rapidly and it happens that oil becomes so thick that the oil pump is not able to feed it to friction couples, resulting in damage or seizure of the engine.
Oils with extended drain intervals are engine oils which can be used to ensure drain intervals longer than the average ones. In general, this concept should be divided into two categories: engine oils with extended drain intervals for passenger car engines and engine oils with extended drain intervals for trucks.
Until recently, typical average drain intervals of engine oils recommended by passenger car engine manufacturers were approx. 10,000 – 15,000 km. Increasing requirements concerning a reduction of vehicle operation and environmental protection costs inevitably lead to such structural solutions of modern engines allowing for both a reduction of the amount of engine oil in an engine lubrication system and extension of oil drain interval. The less amount of oil in the engine lubrication system brings measurable savings for a user, whereas we – as an oil manufacturer – are obliged to meet more strict requirements on its resistance to thermal loads or thermal-oxidation and ageing processes.
When designing modern engines which limit the number of visits at service stations, passenger car manufacturers impose specific requirements to engine oils. The exceptional nature of such requirements results in separate standards developed by them in cooperation with oil manufacturers, which take into account the specificity of respective types and variants of new structures. This is how standards for engine oils with extended drain intervals issued by VW (VW 503.00/503.01, VW 506.00/506.01 standards), BMW (Longlife-04) or GM/Opel (GM-LL-A-025, GM-LL-B-025) were developed.
Engine oils with extended drain intervals, holding appropriate approvals issued by engine manufacturers which confirm their compliance with the above standard, may guarantee drain intervals of 20,000 – 30,000 and even 50,000 km. In some cases, it exceeds previously mentioned typical intervals two or three times
In order to address demands of customers, Tedex offers oils with extended drain intervals and a whole range of high quality oils for all vehicle users.