Basic information from the world of oils

Basic terms and definitions

Viscosity is a level of a resistance of a liquid to flowing.
All oils are classified to viscosity classes according to:

• SAE (motor and gearbox oils)
• ISO (industrial oils)

A lower viscosity puts less resistance to movement but it doesn’t ensure a reliable lubrication.
A higher viscosity lowers the wear of the friction surfaces but increases the energy consumption.
The SAE classification of the motor oils distinguishes 6 winter classes W from 0W up to 25W and 5 summer classes from 20 to 60. For the gearbox oils, there are 3 winter W classes from 75W to 85W and three summer classes from 90 to 250. The summer classes have defined viscosities at 100 °C and winter classes at different temperatures below zero.
The multigrade oils may comprise both, SAE winter and summer classes at the same time.
The ISO classification sorts the oils according to their kinematic viscosity at 40 °C.

Performance level – the capacity to work in difficult conditions.
The performance level is most often given by the API specification for motor and gearbox oils as well as by the ISO specification for industrial oils. The specifications lay down the minimum values for the industrial and engine tests the respective oils has to pass.
In Europe, the specifications of performance levels are also issued by the ACEA – European Automobile Manufacturers’ Association and such significant car makers as MB, MAN, VW, VOLVO etc.

Fuel saving (Full Efficiency) – is achieved by use of less viscosity oils and friction modifiers.

Oil composition
The properties of the lubrication oils depend on their composition. The lubrication oils consists of the basic oil and viscosity and performance additives.
Basic oils are most often petroleum oils but synthetic oils are increasingly expanding (polyalphaoleffins, esters etc.). The basic oils themselves cannot fulfill the requirements of the current specifications and that is why the properties are improved by additives.
Viscosity ingredients increase the viscosity at higher temperatures and only slightly the viscosity at temperatures below 0 °C. As usual, they are polymers.
Performance additives improve the resistance to oxidation, lubricating capacity, detergent and dispersive properties and anti-corrosion protection.

The institutions
SAE (Society of Automotive Engineers) American agency that was found at the beginning of the last century and its specifications is recognized in the whole world.
API ( American Petroleum Institute), American agency that was found at the beginning of the last century and its specifications is recognized in the whole world.
ACEA (Association des Constructeurs Européens des Automobiles) – Association of European Car Makers.
ISO (International Standard Organization) is active in the field of standardization.