Thought I would join in to post what I found yesterday. I'm not sure if anyone has already posted it but this Valvoline oil is CK-4 & ford spec approved WSS-M2C171-F. This is a huge national brand so thought it would be a good idea to post for easier access to the correct oil for our diesel motors. I wanted to change over to the ck-4 but ALSO wanted to make sure I meet fords specs to have the latest & greatest. This was strange b/c valvoline's own website on this oil doesn't state anywhere ck-4. I even called them & they were pretty much clueless about the new product. However, I'm still sold. just look on the upper back of the bottle where it says "Designed for American made heavy duty diesel trucks"... HA! Any questions just ask.
Valvoline 15w-40 Heavy Duty Engine Oil Product Information
Valvoline 15w-40 Heavy Duty Engine Oil Product Information