How to choose an engine oil.
In order to correctly select a motor oil, it is always necessary to follow the vehicle manufacturer's instructions.
Therefore, to identify the most suitable lubricant:
Consult the section on the vehicle use and maintenance manual for the lubricant
-Distinguish the viscosity of the lubricant suggested by the manufacturer (eg 5W30, 15W40)
-Distinguish the performance specifications required by the manufacturer (eg ACEA B4, VW 505.00)
- Identify the viscosity and performance specifications required by the manufacturer among the engine lubricants of the Eni range.
The main requirements that a lubricant must have are:
- Keep the surfaces separated in all load, temperature and speed conditions, thus minimizing friction and wear phenomena
-Actate from cooling fluid by removing the heat produced by friction or coming from external sources
- Be sufficiently stable to guarantee constant behavior for the expected useful life
-Protect surfaces from attack by aggressive products formed during exercise
-Have good detergency and dispersion so as to remove and keep in suspension residues and sludges that may form during the exercise
PROPERTIES OF LUBRICANTS
The main properties of a lubricant, generally reported on the product data sheets, are as follows:
- Viscosity index
- Scroll point
- Flammability point
Viscosity is the resistance that a fluid opposes to the reciprocal sliding of its particles. The viscosity of lubricating oils decreases with increasing temperature and therefore is normally measured at a given temperature (e.g. 40 ° C).
The viscosity of the lubricant determines the thickness of the oil film between the reciprocally moving metal surfaces.
The viscosity unit that is generally used is the centistoke (cSt).
The viscosity index is a characteristic, expressed according to a conventional scale, adopted in the oil industry for the variation of the viscosity of the lubricating oils with the temperature.
In other words, the viscosity index measures the variation of viscosity with the temperature; the higher the value of the lower viscosity index is the variation of the viscosity with the temperature.
Therefore considering two lubricants with the same viscosity at 40 ° C, the one with a higher viscosity index than the other guarantees:
- easier starting at low temperature (less internal friction)
- a degree of separation of surfaces (a thickness of lubricating film) higher at elevated temperatures
The pour point is the minimum temperature at which a lubricant continues to flow when it is cooled. Below the pour point the oil tends to "thicken" and no longer flows freely.
The flash point is the minimum temperature at which the lubricant vapors mixed with air and progressively heated in a standard laboratory receptacle will ignite when a flame approaches.
We can distinguish the point of flammability in a closed vessel (Penskin Martens) and the one in an open vase (Cleveland).
This property as well as to define limits of use and precautions in handling or storage is also useful as an indication of possible contamination by fuels (which have flash points lower than those of lubricants).