Api Automotive Manual Transmission & Asles Classification


Designates the type of service characteristics of manual transmissions operating under such mild conditions of low units pressures and minimum sliding velocities, that untreated oil may be used satisfactorily. Oxidation and rust inhibitors, defoamers, and pour depressants may be used to improve the characteristics of lubricants intended for this service. Frictional modifiers and extreme pressure additives shall not be utilized.


Due to speeds and loads involved, untreated oil is generally not a satisfactory lubricant for many passenger car manual transmissions. For some truck and tractor manual transmissions, untreated oils may be used successfully. In all cases, the transmission manufacturers' specific lubricants recommendations should be followed.



Designates the type of service characteristic of automotive type worm-gear axles operating under such conditions of load, temperature and sliding velocities that lubricants satisfactory forAPI GL-1 will not suffice.


Products suited for this type of service contain anti-wear or very mild xtreme-pressure agents, which provide protection for worm gears.



Designates the type of service characteristic of manual transmissions and spiral-bevel axles operating under mild to moderate to severe conditions of speed and load. These service conditions require a lubricant having load-carrying capacities greater than those thatwill satisfyAPI GL-1 service, but belowthe requirements of lubricants satisfyingAPI GL-4 service.


Gear lubricants designated for API GL-3 are not intended for hypoid gear applications.



Designates the type of service characteristic of spiral-bevel and hypoid gears in automotive axles operated under moderate speeds and loads. These oils may be used in selected manual transmission and transaxle applications. (User should consult axle/transmission manufacturers' specific lubricant recommendations.)


While this service designation is still used commercially to describe lubricants, some test equipment used for performance verification is no longer available. ASTM is investigating the possibility of redefining service designation API GL-4 using modern test equipment.



Designates the type of service characteristic of gears, particularly hypoids in automotive axles operated under high-speed and/or low-speed, high-torque conditions. Lubricants qualified under U.S. Military Specification MIL-L-2105D (formerly MIL-L-2105C) satisfy the requirements of the API GL-5 designation. Details of API GL-5 performance tests are contained is ASTM Publication STP-512A, Laboratory Performance Tests forAutomotive Gear Lubricants Intended forAPI GL-5 Service.



Designates the type of service characteristic of gears designed with a very high pinion offset. Such designs typically require (gear) score protection in excess of that provided by API GL-5 gear oils. A shift to more modest pinion offsets, coupled with the obsolescence of original API GL-6 test equipment and procedure, has greatly diminished the commercial need forAPI GL-6 gear lubricants.


Viscosity Comparisons

Viscosities designated by various organizations may be compared as shown in the table opposite. This is strictly a viscosity comparison and should not be construed as a quality level comparison.

To summarize:
ISO VG - is viscosity measurement in centistokes (cSt) at 40°C.
AGMA - viscosity grades as designated by theAmerican Gear Manufacturers Association.
SAE - Society of Automotive Engineers viscosity measurement for automotive engine and gear oils e.g. SAE 30, SAE 90, etc. Saybolt - These units are in S.U.S. and were used by various refiners/blenders to specify viscosity at 100°F or 21 OOF. How to use the chart :

For instance, if a manufacturer requires an SAE 30 oil for a piece of equipment, go to the SAE viscosity column and follow across horizontally to the left to read an ISO VG of 100.

Viscosity Equivalents

Note :

  • Read across horizontally.
  • Assumes 100 VI single grade oils.
  • Equivalence is in terms of viscosity at 40°C only.
  • Viscosity limits are approximate: For precise data, consult ISO, AGMA and SAE specifications.
  • W grades are represented only in terms of approximate 400C viscosity.
    For low temperature limits, consult SAE specifications.