The lubricant industry relies upon technical standards to ensure consistent levels of quality and performance, regardless of the lubricant manufacturer. End-users should feel comfortable in the belief that if a lubricant carries a performance classification on the label, the contents will provide the protection and equipment life they expect. But is this always the case?

API Category GL-4 was issued more than 50 years ago. While updated performance specifications such as API Category GL-5, API Category MT-1, and the SAE J2360 Standard have superseded it, API Category GL-4 remains active – despite the fact that many in the industry think it should be retired.

Why are API Category GL-4-quality lubricants not the right choice for today’s equipment?

A good starting point is to consider the equipment these lubricants are intended to protect. Since the time that API Category GL-4 was introduced, the design of axles and transmissions, and the demands being placed upon them, has been altered almost beyond recognition:

  • The number of synchronized transmissions has increased, as has the variety of friction materials that are used in them. Some examples of these materials include brass, molybdenum, phenolic resins and carbon.
  • The horsepower of modern engines and the speed at which vehicles are being driven have increased significantly
  • Both light-duty and heavy-duty vehicles are hauling heavier loads than they have in the past
  • Aerodynamic improvements, which deflect cooling air away from the axle and transmission, are resulting in axle and transmission lubricants being subjected to higher operating temperatures
  • The size and weight of axle and transmission components have decreased
  • Axle and transmission sump capacities have been reduced
  • Drain intervals have increased
    What all this means is that there is less fluid in a more hostile environment for longer periods of time.

The above factors are the driving force behind the need for continued quality improvements in modern axle and transmission fluids, and the emergence of higher performance standards to define these improved-quality fluids. Some of these newer performance specifications include:

  • Original Equipment Manufacturer (OEM) specifications for synchronized manual transmission fluids, such as:
    • ZF TE-ML02 , Volvo 97305, and Volvo 97307 for commercial vehicles
    • VW 501.50 and Ford M2C200C for passenger cars
  • API Category GL-5 (ASTM D7450) and the SAE J2360 Standard for axle oils
  • API Category MT-1 (ASTM D5760) for non-synchronized manual transmissions

As can be seen, just meeting API Category GL-4 no longer guarantees that a fluid will provide the level of performance required by modern equipment. If that is so, why is API Category GL-4 still in use? The reason is that it’s a globally-recognized standard, particularly in emerging markets, and because fluids meeting current performance specifications may be slightly more expensive. Equipment operators are hoping to save money by using these lower cost , unvalidated lubricants and may not be considering the true cost of operation associated with using a low-quality product.

It is likely that the nominal savings they make through the use of an inappropriate lubricant will be overshadowed by the cost of repair or replacement of axles and transmissions which have failed due to premature wear and distress. Also to be considered is the loss of revenue which will result from the equipment being out of service while repairs are being made.

How can this problem be addressed?

The answer is through the use of the appropriate lubricant. Most modern axle and transmission manufacturers specify the use of lubricants designed for today’s equipment. This might be an API Category GL-5 or SAE J2360-quality fluid for the drive axle, an API Category MT-1-quality fluid for a non-synchronized manual transmission, or in the case of a synchronized manual transmission, a dedicated transmission fluid approved for use by the equipment manufacturer.

Perhaps it is time that API Category GL-4 was retired for good. It has arguably run its course, and many industry experts believe it should be declared obsolete. The best way for a vehicle owner to insure that he will have the proper protection for his axle and transmission, experience the satisfaction of improved shift quality, and save considerable expense in the long run is to use a lubricant designed for today’s equipment. Clearly, that lubricant will not be one which meets only the requirements of API Category GL-4.

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