API CK-4 will be backward compatible with older diesel engines. The name helps to explain this, as the current category is CJ-4. API CK-4 oils have a minimumHTHS viscosity of 3.5 mPasor higher.API FA-4 oils, however,are intended for next-generation diesel engines,and will have lower high temperature high shear limits (2.9-3.2 mPas).
The new API CK-4 and API FA-4 products are better oils. They will better protect engines, provide better fuel economy, and reduce GHG emissions compared to today’s oils,” explained Shawn Whitacre, chairman of the ASTM Heavy Duty Engine Oil Classification Panel, which developed test methods for the PC-11 category.