American Petroleum Institute (API)

The following information describes API’s automotive gear lubricant, service designations. This system of standards is designed to assist manufacturers and users of automotive equipment in the selection of transmission, transaxle, and axle lubricants based on gear design and operating conditions. Where special performance requirements apply, the descriptions in the publication conform to the automotive lubricants test language developed by the American Society for Testing and Materials (ASTM).

In some axles, some transmissions, and some transaxles, gears of different designs are available for a variety of service conditions. Selecting a lubricant for specific applications involves careful consideration of the operating conditions and the chemical and physical characteristics of the lubricant. The American Petroleum Institute has released lubricant service designations for automotive manual transmissions, transaxles, and axles. Each designation refers to the performance required of 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 may be so designated.

Denotes lubricants intended for axles with spiral bevel gears operating under moderate to severe conditions of speed and load or axles with hypoid gears operating under moderate speeds and loads. These oils may be used in selected manual transmissions and transaxle applications where API MT-1 lubricants are unsuitable.

Denotes lubricants intended for gears, particularly hypoid gears, in axles operating under various combinations of high-speed shock loads and low-speed, high-torque conditions. Lubricants qualified under MIL-L-2105D satisfy the requirements of the API GL-5 specification, although the API designation does not require military approval.

Denotes lubricants intended for non-synchronized manual transmissions used in buses and heavy-duty trucks. Lubricants meeting the requirements of API MT-1 provide protection against the combination of thermal degradation, component wear and oil seal deterioration, which is not provided by lubricants meeting only the requirements of API GL-4 and API GL-5. API MT-1 does not address the performance requirements of synchronized transmissions and transaxles in passenger car and heavy-duty applications.

API Categories GL-1, GL-2, GL-3, and GL-6; were declared inactive by SAE Technical Committee 3 in 1995, even though oils may be marketed with these designations. Similarly, ASTM does not plan to maintain the performance tests associated with these categories, as in a number of cases these tests can no longer be run because parts or test installations are not available.