As we discussed in our last article on SAE J306, this standard is critical when it comes to improving efficiency across all parts of the vehicle. Here, we will take a more in-depth look at this recently-updated standard.
Defining SAE J306 Lubricants
Under the SAE J306 standard, lubricants are defined in terms of a grade denoting their minimum kinematic viscosity at 100˚C, as measured according to ASTM D445, while also demonstrating shear stability as measured by CEC L-45-A99—more commonly known as KRL Shear. This test determines the permanent shear loss of the fluid after 20 hours in a cylindrical roller bearing tester. Wide-span multigrade lubricants typically use performance polymers that are susceptible to shear and if a fluid shears quickly and excessively there is potential for accelerated equipment wear or fatigue. To comply with the SAE J306 Standard, the lubricant must “stay in grade” after shear to maintain the appropriate level of protection.
Some lubricants are further designated with the letter “W,” for Winter, signifying a low-temperature viscosity grade. In addition to their high-temperature definition, these “W” grades are further defined as providing a maximum temperature—ranging from -12 to -55˚C—at which they retain a threshold level of viscosity.
Balancing Blends for Performance
Achieving the optimal lubricant for a given driveline application requires a thorough understanding of both the equipment application and the properties of the base fluid and additive package. Even for a comparatively simple SAE J306-compliant monograde lubricant, performance additives will be used. The additive formulation needs to reduce friction and remove heat, and will include extreme pressure and anti-wear additives to prevent wear and other types of distress that can result in equipment failure and downtime. Protection against oxidation, thermal degradation, rust, copper corrosion and foaming also must be provided.
The viscosity of lubricants tends to decrease with increasing operating temperature:
- At elevated temperatures, the liquid becomes increasingly thin, providing a lower level of protection.
- Conversely, at lower temperatures the fluid thickens and the increased viscosity reduces the efficiency of the equipment it is protecting. For a driveline required to operate only at moderate temperatures, a monograde product may provide adequate protection at an optimal price point.
However, for operation across wider temperature extremes, a multigrade fluid engineered for a more balanced viscosity profile is required. To achieve the required performance, multigrade fluids need additional additive components. Depending on the extent of cold-temperature operation, multigrade lubricants will, for example, require the addition of a pour point depressant, and for optimal efficiency, additional performance polymer.
Importance of Pour Point Depressants and Performance Polymers
In cold temperatures, the wax in base oil tends to separate out and form crystals that interlock and lead to fluid thickening. As the fluid drops below the pour point, this thickening increases significantly, leading to increased mechanical losses in the equipment as well as reduced lubricant effectiveness. Pour point depressants modify the shape of the wax crystals that form at low temperature, preventing them from interlocking and thus reducing the pour point by as much as 40˚C.
The selection of the correct pour point depressant will be influenced by the choice of base oil, the potential interaction with the performance additive package and any performance polymer used, along with the performance requirements and operating environment of the equipment.
The performance polymer must also be selected to ensure compatibility with the other lubricant components. For many specific applications, a range of polymer structures have been developed to provide the desired performance. Selection of the right product for the right application is crucial in order to avoid compromising equipment performance and durability.
For more information on SAE J306, contact your Lubrizol representative.