Transmission oil
API Classes
Transmission oil (or gear oil) is classified according to the API (American Petroleum Institute) in GL and MT ratings.
- GL-1 - Deprecated: Used for mild conditions and low unit pressures. Contains oxidation and rust inhibitors, defoamers and pour depressants.
- GL-2 - Deprecated: Used for worm-gear-axles and for conditions of load, sliding and temperatures where GL-1 wouldn't suffocate.
- GL-3 - Deprecated: Used for spiral-bevel-axles in mild to moderate conditions.
- GL-4 - Used for spiral-bevel and hypoid gears with moderate speeds and loads.
- GL-5 - Used for spiral-bevel and hypoid gears with high speed and high torque.
- GL-6 - Obsolete: Designed for very high pinion offset.
- GMT-1 - Used for non-synchronized manual transmission like buses and heavy-duty trucks. Exceeds the protection requirements of GL-4 and GL-5.
OEM Specifications
Honda states that you should use Honda MTF which is specified as:
- 75W-80 viscosity
- Meets GL-4 Spec
2nd Gear grinding
See: Second gear grinding
Recommendations
Generally speaking you want:
- Meet or exceed the OEM specification
- The highest possible flashing point
- The lowest possible pour point
Castrol Syntrans FE 75W
This oil has fixed the 2nd gear grinding problem for several people. It also meets all the required OEM criteria.
| Flash Point, ºC (ASTM D92) | 226 |
| Pourpoint, ºC (ASTM D97) | -51 |
| Density, @15ºC, g/ml (ASTM D4052) | 0,852 |
| Viscosity, @40ºC, (ASTM D445) | 32,2 |
| Viscosity, @100ºC, (ASTM D445) | 6,3 |
| Viscosity index (DIN ISO 2909) | 154 |
| API | GL-4 |