![]() Similar guidelines are used for gears, bearings, engines, etc., to assure the lubricant flows to the various components at low temperature start-up and protects against wear at operating temperature.įigure 1 demonstrates the various temperature operating ranges for a given operating viscosity range. OEMs also specify the minimum viscosity for the system during operation to minimize metal-to-metal contact and wear. Hydraulic pump OEMs identify the maximum viscosity allowed at system start-up to ensure the fluid will flow and avoid pump damage due to cavitation (see the February 2022 TLT Lubrication Fundamentals article titled Air entrainment, aeration, cavitation and foaming: How are they related?). The temperatures at which the oil reaches the maximum and minimum allowable viscosities determines the operating range. Thus, original equipment manufacturers (OEMs) specify maximum and minimum allowable viscosities to protect their equipment. This is important because lubricated equipment is subject to extreme temperatures: cold at start-up until the unit has warmed up, potentially to extremely hot at times. Non-EP lubricant grades are rust and oxidation inhibited, only EP Lubricants are mild Extreme Pressure type.Oil viscosity varies with temperature so much so that an oil’s viscosity should always be qualified with the temperature at which the viscosity is measured. Note: Compounded oils must have 3-10% suitable animal fats. ![]() The American Gear Manufacturers Association (AGMA) and the International Standards Organization (ISO) have established viscosity standards for hydraulic fluids and industrial gear lubricants.įollowing are the AGMA Lubricant Numbers, the corresponding ISO Grade and the viscosity ranges: Axle and Manual Transmission Lubricant Viscosity ClassificationĪGMA and ISO Viscosity Grade Classifications.Following is a table with the SAE gear lubricant viscosity grades: 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. 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. Gear lubricant viscosity grades should not be confused with engine oil viscosity grades. The Society of Automotive Engineers (SAE) has devised a method for classifying the viscosity characteristics of gear lubricants as well. Following is the API description: SAE Viscosity Grades for Gear Lubricants ![]() 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. ![]() Viscosity Temperature Chart API Service Designation for Gear Lubricants SAE Viscosity Grades for Engine Oils – SAE J300 Dec 99 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 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.
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