GL is API’s (American Petroleum Institute’s) designation for “Gear Lubricant” and contains several numbered sub categories that describe characteristics and application.
Current service designations, (obsolete where indicated.)
| GL-1 | Light duty lubricant intended for manual transmissions operating under mild conditions such that petroleum or refined petroleum oil may be used satisfactorily. The following maybe added to improve operating characteristics: – Oxidation Inhibitor(s) – Rust Inhibitor(s) – Defoamers – Pour Depressants |
| GL-2 | Light EP for worm gears |
| GL-3 | Light EP for spur & spiral bevel gears for axles and transmissions |
| GL-4 | Medium EP, MIL-L-2105 quality, moderate severity hypoid gears, manual transmissions. Denotes lubricants intended for axles with spiral bevel gears operating under moderate to severe conditions of speed and load. also covers axles with hypoid gears in moderate speeds and loads. These lubricants might be used in selected manual transmission and transaxle applications. |
GL-5 | High EP, MIL-L-2105D quality, all hypoid axles, some manual transmissions |
+GL-5 | Denotes lubricants intended for gears, particularly hypoid gears, in axles operating under various combinations of high-speed, low-speed, high-torque, and shock-load conditions. Lubricants qualified under U.S. Military Specification MIL-L-2105E (formerly MIL-L-2105D) satisfy the requirements of the API GL-5 service designation. Performance test details are in ASTM Publication STP-512A, “Laboratory Performance Tests for Automotive Gear Lubricants Intended for API GL-5 Service.” API GL-5 quality gear lubricants possess adequate extreme pressure characteristics for essentially all automotive gear applications to prevent wear, pitting, scoring and ultimate gear failure, along with protection against oxidation, thermal degradation, rust, copper corrosion, foaming and water emulsification (pay attention mud and water wheelers). API GL-5 oils most widely used automotive gear lubricants in North America for passenger cars, trucks, bus and heavy construction equipment. |
GL-6 | Extra high EP, now obsolete |