Lower HTHS
“One way to improve fuel economy of heavy-duty diesel engines, which are still largely hydrodynamic in lubrication, is to reduce the high-temperature, high-shear [HTHS] viscosity of the engine oil,” said Steve Haffner, North American market manager for Infineum USA. “All things being equal, just reducing the viscosity of the oil also reduces the film thickness on critical engine parts. Reduced film thickness can lead to reduced durability. Since OEMs and consumers are focused on getting the maximum useful life out of diesel engines while also maintaining fuel efficiency, new engine oils have been formulated to balance delivering enhanced fuel economy while maintaining or enhancing engine durability.”
Users should look for oils that meet OEM and API specifications and are supported by additive technology that has been field tested to demonstrate proven performance in real world applications.
Tony Negri, director of commercial products for Phillips 66, is in agreement. “The major factor distinguishing FA-4 oils from their CK-4 counterparts is that their HTHS shear values,” he said. “HTHS is an additional measure of viscosity representing internal fluid friction—the lower this value, the better the fuel economy versus an oil of the same kinematic viscosity [expressed as centistokes or cSt] with a higher HTHS. In other words, there will be SAE 10W-30 oils in both the CK-4 and FA-4 categories with their main differentiator being their HTHS values. Where CJ-4 and CK-4 require a minimum HTHS of 3.5 cP [centipoise], FA-4 oils will feature HTHS values in the range of 2.9–3.2 cP.”
Additive packages
“Additive and performance polymer packages as part of the finished lubricant have both an indirect and a direct impact on improved fuel economy and emissions benefits through the use of higher performance lubricants,” said Paul Basar, Lubrizol’s regional business manager for heavy-duty diesel engine oils. “Compatibility with aftertreatment devices such as diesel particulate filter and selective catalytic reduction in API CJ-4 is carried over to API CK-4 and API FA-4.”
Basar added that API CK-4 oils inherently offer improved oxidation resistance in use in today’s hotter-running engines compared to API CJ-4 oils. As oils oxidize, they become thicker and this degrades fuel efficiency during the drain interval.
With API CK-4 and FA-4 oils, this effect is greatly lessened; so all the new oils will provide better fuel economy durability performance while at the same time increasing overall engine protection.
“The new API FA-4 engine oils (as with API CK-4 oils), have been formulated to provide greater protection for all engines through increased oxidative stability, increased resistance to aeration and increased shear stability,” Basar continued. “Additionally, API FA-4 oils have to be designed and tested to achieve a HTHS limit of 2.9-3.2cP, offering increased fuel economy benefits and reduced. New API FA-4 oils which have a lower high-temperature, HTHS also offer the potential for additional fuel economy improvements, typically of 0.5-1% on a like-for-like viscosity basis, which financially can equate to significant savings for the fleet over the lifetime of every vehicle.”
The final word
Following a recent announcement from the EPA to vehicle manufacturers, new vehicles that are API FA-4 compatible will have to clearly state “API FA-4 oils” on the oil filler cap. This will also be stated in the service and maintenance manual. This will make it easier for maintenance teams to visually see which new vehicles should be using API FA-4 engine oils, together with any additional OEM approvals that may be relevant to the fleet.
