For sure you should be using API CI-4 HD diesel engine oil in any engine without a catalyst. Many vintage Mercedes owners have been using CI-4 in gasoline engines for a long time with no obviously apparent degradation of the catalyst.

CI-4 will be replaced by CJ-4 in about a year, and it looks like CJ-4 will have a limit on phosphorous content, which will limit ZDDP.

There's a recent article on the subject at:

www.LMTRUCK.com

Duke