Differential 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
- Hypoid gear oil
- API GL-5 or GL-6
- Viscosity: SAE 90
Recommendations
Generally speaking you want:
- Meet or exceed the OEM specification
- The highest possible flashing point
- The lowest possible pour point
Castrol Syntrax Long Life 75W-90
| Flash Point, ºC (ASTM D92) | 224 |
| Pourpoint, ºC (ASTM D97) | -57 |
| Density, @15ºC, g/ml (ASTM D4052) | 0,858 |
| Viscosity, @40ºC, (ASTM D445) | 101 |
| Viscosity, @100ºC, (ASTM D445) | 15,4 |
| Viscosity index (DIN ISO 2909) | 161 |
| API | GL-5 |
Mobil1 SHC 75W-90
| Flash Point, ºC (ASTM D92) | 202 |
| Pourpoint, ºC (ASTM D97) | -54 |
| Density, @15ºC, g/ml (ASTM D4052) | 0,87 |
| Viscosity, @40ºC, (ASTM D445) | 102 |
| Viscosity, @100ºC, (ASTM D445) | 15,1 |
| Viscosity index (DIN ISO 2909) | 156 |
| API | GL-5 |