Originally Posted By: Invasivore
Yes, I would like to know if adding the bottle of ZDDP will negatively affect film strength, suspension of other additives, and effectiveness of other additives.
That's a very good question. To you and to Ether, as best as I recall, ZDDP has more than one function as an additive (or more accurately, additives), including not just anti-wear but as an anti-oxidant.
Just like an HDEO isn't an automatic substitute for a race oil for a gasser, I'd suspect a ZDDP additive designed for performance gasoline engines may not turn a lower phosphorus HDEO into a CI-4+ automatically. I wouldn't go so far as to talk about additive clash, but the intended benefits may just not be there.
Heck, as I recall, at least one car journalist (can't remember if it was print or TV off hand) found out the hard way that a ZDDP additive to an ordinary motor oil can at times be a poor substitute for a dedicated break in lubricant. I don't think we'd find that by running a CK-4 lubricant with a ZDDP additive, but there really isn't any evidence that the additive is needed in the first place.
For those who are worried, I suppose Ford's list is a good place to start. Of course, we are seeing CK-4 only oils, rather than dual rated options, too. I certainly understand everyone's concern. A diesel engine going south isn't like tossing in a cam and set of lifters into a 305 for $200 and an afternoon of work. However, sooner or later, CK-4 will be the only readily available product, and that's probably the case in some places by now.