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