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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.
- Hypoid gear oil
- API GL-5 or GL-6
- Viscosity: SAE 90
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|
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|