Viscosity classification
SAE-class for Engine Oils and Transmission Oils
(SAE = Society of Automative Engineers)
ISO-class for Industrial Lubricating Oils
(ISO = International Standards Organisation)
There have been many different measurement units to express the viscosity or lubricating oils, such as Engler degrees, Saybolt Universal Seconds (SUS), or centistokes (cSt). The temperature was stated at different levels in Celsius or Fahrenheit. Today, international standards require that the measurement unit is expressed in mm2/s (cSt) and that the temperature is expressed in Celsius degrees.
By international cooperation, approval was reached in 1975 for the new ISO classes. It meant a simplification of the conception viscosity for industrial lubricating oils. In the same way, the long established and well-known SAE classes for engine oils and transmission oils was created. Every ISO class and SAE class state a fixed clearly defined viscosity range at a certain temperature. In general, the higher the number of the class, the higher the viscosity. The classes do not however give any indication as to the quality of the oil.
