What changed with CK-4 oil?

[Nilao]

I found an interesting TSB from Ford MoCo



Ford Motor Company CK-4/FA-4 Ford Position Statement
Starting on December 1, 2016 the American Petroleum Institute (API) will begin licensing
two new diesel motor categories CK-4 and FA-4. API CK-4 is being released to replace
CJ-4. FA-4 is a low viscosity diesel oil released for diesel engines designed for a lower
viscosity oil.
API FA-4
Due to its low viscosity FA-4 should not be used in any Ford diesel vehicles at this time.
API CK-4
Ford will not be recommending the use of CK-4 motor oils in any Ford diesel engines,
new or old. Testing Ford has done on some CK-4 formulations have shown inadequate
wear protection compared to CJ-4 formulations developed and licensed before 2016.
Like many other diesel engine manufacturers, with their own internal OEM specification,
Ford will now be recommending oils that meet an OEM specification, Ford Material
Engineering Specification WSS-M2C171-F1. The customer should use an oil showing
that it meets this specification.
An oil showing CJ-4 in the API donut without showing CK-4 would be acceptable for
service even if not showing WSS-M2C171-F1. This oil would most likely be an older CJ-
4 formulation, developed and licensed prior to 2016. These oils could be around for
about a year after CK-4 licensing begins, December 1, 2016. Field experience and Ford
testing has shown that these older CJ-4 formulations provide acceptable 6.7L engine
protection.
To insure you protect your Ford diesel engine use an oil meeting Ford specification
WSS-M2C171-F1 like Motorcraft Super Duty Motor oil.