The Society of Automotive Engineers (SAE) viscosity grading system for engine oils consists of “W” grades that define low temperature viscosities and “straight” grades that put further limits on high temperature viscosities. The chart shown at the bottom of the page graphically represents the viscosity-temperature relationship of the SAE grading system with lines drawn to show the viscosity characteristics for several popular motor oils.
The automotive and petroleum industries in cooperation with the American Society of Testing and Materials (ASTM), Society of Automotive Engineers (SAE) and the American Petroleum Institute (API) have developed a service classification system to serve as a guide for recommending and marketing gear lubricants. Following is the API description:
The Society of Automotive Engineers (SAE) has devised a method for classifying the viscosity characteristics of gear lubricants as well. Gear lubricant viscosity grades should not be confused with engine oil viscosity grades. A gear lubricant and an engine oil having the same viscosity will have widely different SAE viscosity grade designations as defined in the two viscosity classifications. For instance, an SAE 80W gear lubricant may have the same viscosity as an SAE 20W or SAE 30 engine oil and SAE 90 gear lubricant viscosity can be similar to that of an SAE 40 or SAE 50 engine oil. Following is a table with the SAE gear lubricant viscosity grades:
The American Gear Manufacturers Association (AGMA) and the International Standards Organization (ISO) have established viscosity standards for hydraulic fluids and industrial gear lubricants.
Following are the AGMA Lubricant Numbers, the corresponding ISO Grade and the viscosity ranges: