The American Petroleum Institute has developed specific lubricant service designations for automotive manual transmissions and axles, each designation referring to the performance required from a gear lubricant for a specific type of automotive service. These designations also recognize the possibility that lubricants may be developed for more than one service classification and consequently may be so designated. The system of designations replaces all previous API gear lubricant designations.
API GL-1 --Designates the type of service characteristics of automotive spiral-bevel and worm gear axles as well as some manually operated transmissions operating under such mild conditions of low unit pressures and sliding velocities that straight mineral oil can be used satisfactorily. Oxidation and rust inhibitors, defoamers and pour depressants may be utilized to improve the characteristics of lubricants for this service. Frictional modifiers and extreme pressure agents shall not be utilized.
API GL-2 --Designates the type of service characteristics of automotive type worm gear axles operating under such conditions of load, temperature and sliding velocities that lubricants satisfactory for API GL-1 service will not suffice. (obsolete)
API GL-3 --Designates the type of service characteristics of manual transmissions and spiral-bevel axles operating under moderately severe conditions of speed and load. These service conditions require a lubricant having load carrying capacities greater than those which will satisfy API GL-1 service, but below the requirements of lubricants satisfying API GL-4 service. (obsolete)
API GL-4 --Designates the type of service characteristics of gears, particularly hypoid in passenger cars and other automotive equipment operated under high-speed: shock-load, low-torque, and low-speed: high-torque conditions.
API GL-5 --Designates the type of service characteristics of gears, particularly hypoid in passenger cars and other automotive equipment operated under high-speed: shock-load, low-torque, and low-speed: high-torque conditions.