Driveline Additives

API GL-5 Clearing up the confusion

Assuring that gear oils are up to the challenge

Just as the operating demands on vehicles vary widely, so too do the demands on the gear lubricants that must keep axles and manual transmissions functioning flawlessly and reliably.

Variations in speed, torque and other operating conditions all present different challenges under real-world conditions. The more exacting the demand for performance, the more essential it is that lubricants rise to the challenge.

The continuous development and clarification of industry specifications – supplemented by original equipment manufacturers’ own standards for their unique requirements – reflects the distinct performance requirements of today’s vehicles and their end users.

Clearly defined industry performance specifications are intended to enable OEMs, end-users, oil marketers and lubricant additive manufacturers anywhere in the world to speak the same language when it comes to lubricants. The standards are your assurance that gear oils are up to the challenge, so it’s important to understand what they mean.

What’s the difference?

The performance requirements for automotive gear lubricants depend on their intended use.

  • API Category GL-1 (inactive*) designates the type of service characteristic of manual transmissions operating under such mild conditions of low unit 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. Friction modifiers and extreme pressure additives shall not be used.
  • API Category GL-2 (inactive*) 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 for API GL-1 service will not suffice.
  • API Category GL-3 (inactive*) 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 that will satisfy APL GL-1 service, but below the requirements of lubricants satisfying the API GL-4 service.
  • API Category GL-4 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.
  • API Category GL-5 designates the type of service characteristic of gears, particularly hypoids in automotive axles under high-speed and/or low-speed, high-torque conditions. Lubricants qualified under U.S. Military specification MIL-L-2105D (formerly MIL-L-2015C), MIL-PRF-2105E and SAE J2360 satisfy the requirements of the API GL-5 service designation.
  • API Category GL-6 (inactive*) 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. The original API GL-6 test equipment is obsolete.
  • API Category MT-1 designates lubricants intended for non-synchronized manual transmissions used in buses and heavy-duty trucks. Lubricants meeting API MT-1 provide protection against the combination of thermal degradation, component wear, and oil seal deterioration which is not provided by lubricants meeting only the requirements of API GL-4 and API GL-5.
  • MIL-PRF-2105E this specification released in 1995 combines the performance requirements of its predecessor (MIL-L-2105D) and API MT-1. MIL-PRF-2105E maintains all existing chemical/physical requirements, stationary axle test requirements, field test requirements and data review by the Lubricants Review Institute that were required under MIL-L-2105D. It also adds the stringent oil seal compatibility and thermal durability test requirements under API MT-1. MIL-PRF-2105E has been re-written as SAE Standard J2360.
  • SAE J2360 standard is a new global quality standard that defines a level of performance equivalent to that defined by MIL-PRF-2105E, a U.S. military standard for approval that was not available to oil blenders in all parts of the world. It includes all of the most recent axle and transmission testing requirements identified in API GL-5, API MT-1, and MIL-PRF-2105E including the need to demonstrate proof-of-performance through rigorous field testing.

* API Categories GL-1, GL-2, GL-3 and GL-6 were declared inactive by SAE Technical Committee 3 in 1995, even though oils may be marketed with these designations. Similarly, ASTM does not plan to maintain the performance tests associated with these categories, as in a number of cases these tests can no longer be run because parts or test installations are not available.

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API GL-5: The building block to change

API GL-5 The building block to change
More and more, end-users worldwide are finding that the performance defined by API GL-5 is the practical minimum to deliver acceptable performance and equipment dependability. As a result, API GL-5 may be regarded as the industry’s fundamental building block in growing numbers of the world’s regions. The tests indicated on the following table provide end-users the assurance of a basic level of gear oil performance.

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API GL-5: An update, not a new standard

Confusion and ambiguity that once surrounded the API GL-5 standard should rapidly be alleviated, thanks to a forthcoming rewrite – or update – of the standard.

Previously, some users found it difficult to access the test equipment and ASTM STP 512A, which was the book that contained the API GL-5 test information, and was primarily a compilation of test procedures. The update is in the form of an ASTM Standard, easily accessible to anyone who needs it.

In addition, there was no process in place to periodically review and update the standard. As a result, references to certain test methods became outdated and there was potential for confusion regarding what constitutes an acceptable result. The update includes current test procedures and reference oils, and designation as an ASTM Standard requires review and revalidation every five years.

The rewrite is the result of more than one year of work by a technical committee of ASTM International, one of the world’s largest voluntary standards development organizations. The committee included representatives of oil marketers, dependent and independent testing facilities, the military and additive manufacturers, including Lubrizol.

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Beyond API GL-5

Beyond API GL-5

Increasingly, original equipment manufacturers and end-users are seeking lubricant performance qualities that exceed those of API GL-5. The SAE J2360 is an example of a standard that defines a level of performance beyond API GL-5.

By far the premier standard in common use today, SAE J2360 is a global quality standard specified by many North American OEMs and by growing numbers elsewhere in the world. The rigorous approval requirements, including controlled field testing and independent committee review, ensure that products approved under the SAE J2360 Standard meet the very highest demands of axles and non-synchronised manual transmissions.

SAE J2360 will have a significant impact in parts of the world where the MIL-PRF-2105E specification has not been available. The lack of a global performance standard has resulted in various degrees of quality throughout the world. The lack of uniform quality is regarded by many as the cause for warranty issues for OEMs and equipment problems for end-users. The transition to SAE J2360 should result in an overall increase in performance level for automotive gear lubricants globally.

In 1986, the SAE outlined the trucking industry's need for a gear lubricant category which would provide performance characteristics essential to ensure optimum service life for heavy-duty non-synchronised manual transmissions. It was determined the class of oils used in manual transmissions was not always in compliance with the builder's primary recommendations. API Category MT-1 was developed to satisfy OEM objectives for optimum transmission performance and service life. This was achieved by combining in a single lubricant the cleanliness and oil seal life typical of engine oils with the load characteristics of gear oil.

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Ask the right questions

  • Getting the kind of vehicle performance you expect begins with asking the right questions – and getting the right answers – about lubricant products. Here are a few to ask your supplier.
  • Does my lubricant provide the level of performance recommended by the equipment manufacturer for the type of service I need?
  • What tests were used to evaluate this lubricant, and what relevance do these tests have to my equipment and/or its operation?
  • Why do I need to worry about the “level of performance” of my lubricant? I’m using an SAE 80W-90 grade oil, just like my OEM recommends. Doesn’t my SAE 80W-90 oil provide all the performance I need?
  • Would my equipment perform better or last longer if I used a better-quality lubricant?
  • Can you provide test data to confirm that the lubricant I’m buying meets the performance requirements that you claim? How can I be sure that the test data is legitimate?
  • May I see the Qualification Number and Qualified Products List for this product? (For products approved under the SAE J2360 Standard) 

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