API automotive gear-lubricant service designations
API Publication 1560, Lubricant Service Designations for Automotive Manual Transmissions, Manual Transaxles, and Axles, identifies API GL-5 as the only API automotive gear-lubricant service designation in current use. API GL-1, GL-2, GL-3, GL-4, GL-6, and MT-1 are retained below for historical and compatibility reference, but API no longer considers them current designations.
An API gear-lubricant category describes performance for a defined type of service; it is not a viscosity grade and is not a universal vehicle approval. Gear-oil viscosity grades are defined separately by SAE J306. Always verify the required fluid specification, viscosity grade, and any axle, transmission, synchronizer, or limited-slip requirement in the current vehicle or equipment manufacturer documentation.
| Designation | API status | Description and compatibility context |
|---|---|---|
| API GL-5 | In current use | For gears, especially hypoid gears in axles, operating under combinations of high-speed/shock loading and low-speed/high-torque conditions. ASTM D7450 defines the API GL-5 performance requirements. Limited-slip axle friction requirements are normally set by the axle manufacturer. |
| API GL-1 | Not in current use | Historically intended for manual transmissions under very mild conditions where straight mineral oil could be satisfactory. Oxidation inhibitors, rust inhibitors, defoamers, and pour-point depressants could be used, but friction modifiers and extreme-pressure additives were excluded. It is generally unsuitable for most passenger-car manual transmissions. |
| API GL-2 | Not in current use | Historically intended for automotive worm-gear axles where GL-1-level lubrication was insufficient. Products for this application used anti-wear or film-strength additives designed for worm-gear protection. |
| API GL-3 | Not in current use | Historically intended for manual transmissions under moderate-to-severe conditions and spiral-bevel axles under mild-to-moderate speed and load. Its load-carrying capability was above GL-1 but below GL-4. It was not intended for hypoid axles. |
| API GL-4 | Not in current use | Historically intended for spiral-bevel axles under moderate-to-severe conditions and hypoid axles under moderate speed and load. It has also been used in selected manual transmissions and transaxles. Although GL-4 remains a commercial label, API states that the test equipment needed to verify performance is no longer available; obtain supporting documentation where a legacy GL-4 claim is relevant. |
| API GL-6 | Not in current use | Historically intended for gears with very high pinion offset that required greater scoring protection than GL-5. Reduced use of such gear designs and the obsolescence of the original test equipment and procedures greatly reduced its commercial relevance. |
| API MT-1 | Not in current use | Historically intended for non-synchronized manual transmissions in buses and heavy-duty trucks. It addressed thermal degradation, wear, and oil-seal deterioration beyond that provided by lubricants meeting only GL-4 or GL-5. It does not define the requirements of synchronized transmissions or transaxles, and it should not be treated as a general manual-transmission-fluid approval. |
Related current standards
| Standard | Role | Relationship to API designations |
|---|---|---|
| ASTM D7450-24 | Performance specification for rear-axle gear lubricants intended for API GL-5 service. | Provides the performance basis for API GL-5 service. |
| SAE J2360 (May 2022, reaffirmed December 2025) | Higher-performance automotive gear-lubricant standard for commercial and military use. | SAE J2360 lubricants satisfy API GL-5 and include additional requirements, including elastomer compatibility and gear cleanliness after oxidation. It is intended principally for hypoid-type automotive gear units and is not suitable for worm gears. |
| SAE J306 (February 2025) | Automotive driveline-lubricant viscosity classification. | Defines viscosity limits only; an SAE viscosity grade does not establish API GL performance or vehicle-manufacturer approval. |
Selection notes
A limited-slip differential may require a specific frictional performance level or additive treatment specified by the axle manufacturer; API GL-5 alone does not define that requirement.
Automatic and semi-automatic transmissions, torque converters, fluid couplings, and tractor hydraulic systems commonly require purpose-designed fluids rather than an API automotive gear lubricant.
A product carrying multiple claims is not automatically suitable for every transmission, transaxle, transfer case, or axle application. See why an API GL-4 or GL-5 label is not a universal approval.
For broader background on the standards body, see the American Petroleum Institute specification page.