In April of 2013, the Society of Automotive Engineers (SAE) introduced a new, low viscosity grade specification in revisions made to the J300 Engine Oil Classification. Formally labeled as SAE 16, the new oil specification will help OEMs meet increasingly strict corporate average fuel economy (CAFE) requirements. However, ultra-low viscosity grade oils can create durability challenges.
SAE 16 will serve as a lighter-weight alternative to SAE 20. With kinematic viscosity (KV) limits set at 6.1 — 8.2 mm2/s at 100°C, the main objective behind SAE 16 is to better facilitate fuel efficiency in engines by reducing hydrodynamic friction between moving parts, such as piston rings, bearings and valve trains.
To further contribute to higher fuel economy, a reduction in the oil’s high-temperature, high-shear (HTHS) viscosity limits has also been defined in SAE 16. Set at a minimum of 2.3 mPa⋅s at 150°C, this marks the first time ever that SAE has defined this limit below 2.6. Although it will help improve fuel efficiency throughout the entire oil drain interval, it opens the door for increased wear and tear on critical engine parts. This makes the development of new additives suitable for ultra-thin oils in high power density engines that much more critical.
In addition to the introduction of SAE 16 last April, the new revision to J300 also included a change in the minimum high-temperature viscosity range of SAE 20. With a previously set KV minimum limit measured at 100°C of 5.6 mm2/s, the lower portion of the SAE 20 range was not being utilized by OEMs. As a result, the limit was raised to 6.9 mm2/s, which effectively narrowed SAE 20’s range and made it similar to that of higher-viscosity grades.
The revisions made to the J300 Classification Standard have paved the way for low viscosity SAE XW-16 oils. This will have a significant impact on the GF-6 engine oil performance category, especially because of its proposed split into two separate subcategories: GF-6A and GF-6B.
While GF-6A oils (i.e., SAE 0W-20) will incorporate all the measures of protection required for use in gasoline direct injection (GDI) engines, along with other innovative automotive technologies that haven’t yet reached the market, it will be backwards compatible with all applications currently approved for GF-5. As a result, the viscosity of these oils will be low but not so low that they can’t protect against wear and corrosion in older engines.
GF-6B, on the other hand, forgoes the requirement to be backwards compatible with GF-5 applications and opens the door for the development of ultra-low viscosity lubricants (i.e., SAE 16) that will push the industry into areas of formulation that have never before been encountered. These lubricants will produce significant fuel economy benefits for many engine applications, but because of their low viscosity grade, there is the potential for wear or other durability related issues.
When asked about the implications that SAE XW-16 will have on passenger car motor oil (PCMO) performance requirements, Lubrizol’s PCMO Product Manager, Jon Vilardo, said:
“While it is generally accepted that lower viscosity brings an improvement in fuel economy performance, it can have a negative impact on durability; the protective oil film is less robust, or under the most extreme loading conditions, non-existent. In terms of performance requirements, this translates to a set of standards that will ensure fuel economy is improved via lower viscosity, but durability will not be compromised. The future proposed ultra-low viscosity GF-6B specification requires the same durability performance as the proposed GF-6A. This may require enhanced fortification of specific additive components or a different formulation shape to deliver the required durability in SAE XW-16 fluids.”
Recognizing this, Lubrizol has already begun product development on a specially formulated additive to meet ultra-low viscosity durability demands, especially in anticipation of API SN soon becoming a licensable spec for SAE XW-16 oils.
Pushing the limits of engine oil formulation, the objective of this new additive will be to meet future market needs and allow for the use of low viscosity lubricants in highly demanding engine applications, without the inherent complications they present in terms of protection and durability. Other design goals will be to provide improved high temperature deposit protection for pistons, better sludge control and seal compatibility.