Most fleets rely on CK-4, and for good reason. It is familiar, trusted, and approved for a wide range of engines. FA-4, on the other hand, tends to get less attention, even though it can deliver real fuel-economy benefits in the engines designed for it. With holiday hauling and long-distance runs picking up, it is worth taking a moment to re-familiarize ourselves with where FA-4 fits.
CK-4 vs. FA-4: What is the difference?
Even though CK-4 and FA-4 serve different roles, both categories go through the same rigorous performance testing. FA-4 oils must pass the same tests at the same thresholds as CK-4. They simply do it at lower high-temperature and high-shear (HTHS) viscosity values. That is what gives FA-4 its fuel-economy advantage in supported engines.
Where FA-4 Makes Sense
FA-4 is not a universal replacement for CK-4. But for fleets running late-model engines that are approved for lower-viscosity formulations, FA-4 can help reduce operating costs by improving fuel economy. Many fleets with mixed equipment choose to run CK-4 in older engines and FA-4 in newer platforms, which is a practical and real-world approach.
Why Consider Kendall Super-D FE?
For engines designed for FA-4, Kendall Super-D FE helps deliver:
- Better fuel economy compared to conventional HDEO
- Strong wear protection, including performance comparable to Super-D XA on the DD13 Scuffing Test (ASTM 8074)
- Outstanding oxidation resistance for cleaner operation and longer oil life
- Better low-temperature flow for cold starts
- Effective soot and deposit control
Looking Ahead
With PC-12 on the horizon and new testing underway, understanding where FA-4 fits today helps fleets prepare for what is next. For engines approved to use it, FA-4 can be one of the fastest and most affordable ways to squeeze more efficiency out of long-haul and regional-haul routes.
If holiday miles are adding up and you are weighing fuel savings, uptime, and long-term operating costs, Super-D FE is worth a closer look for the parts of your fleet built for it.
