As Original Equipment Manufacturers (OEM) seek ways to improve efficiency across almost every part of the vehicle, automotive gear lubricants continue to play an important role. Lower viscosity automotive gear lubricants can improve fuel efficiency and reduce greenhouse gas emissions by reducing churning power loss and improving operating efficiency in the appropriate application.

The Society of Automotive Engineers (SAE) is synonymous within the lubricants industry as the internationally recognized and popularly accepted classification and categorization system for lubricants, with the SAE J306 Standard being a key specification for automotive gear lubricants. This standard defines the limits for a classification of automotive gear lubricants in rheological terms—i.e. the lubricant’s flow and deformation. It is intended for use by OEMs in defining and recommending automotive gear, axle and manual transmission lubricants.

In contrast, engine lubricant viscosity classification is defined by the SAE J300 standard. These applications represent product categories that are significantly different and which fulfil completely different sets of requirements. It is therefore essential that the grade scales defined under the SAE J306 and J300 standards are not compared or confused, as the use of an inappropriate fluid can lead to catastrophic and highly expensive equipment failure.

SAE J306 last saw major revisions in 2005, meaning today’s requirements for lower viscosity automotive gear lubricants were not adequately reflected. Effective February 2019, SAE J306 has been updated in order to adequately define current and future low viscosity fluids. The revised standard better outlines the low viscosity grades for future manual transmission fluid and automotive gear oil requirements through the introduction of three new viscosity grades:

• SAE 65
• SAE 70
• SAE 75

At the same time, the SAE 80 viscosity grade has been amended to tighten the broad kinematic viscosity window which previously existed. Lowering the minimum kinematic viscosity limit from 7.0 cSt to 3.8 cSt at 100°C allows for new lubricants as low as SAE 65 to be utilized in conjunction with more modern hardware designs. The revision also affects the lower viscosity limits of SAE 70W, SAE 75W and SAE 80W as can be seen here.

Our View

The SAE J306 revision with precise viscosity bands gives a framework to develop low viscosity fluids with the appropriate balance of efficiency and durability. The introduction of new lower viscosity grades provides the opportunity for more efficient automotive gear lubricants to work in harmony with advanced hardware designs, where the lubricant enables hardware design improvements as well as directly contributing to increased efficiency through its lower viscosity characteristics.

For more information on SAE J306, contact your Lubrizol representative.