If you use synthetics, Delvac-1 is about the best diesel synthetic you can possibly buy, with Amsoil 15W-40 in second place, and Mobil-1 15W-50 in third place (all are EXCELLENT oils). But you DO NOT want to use SynTec, Rotella Syn, or Delo Syn - these are not true synthetics (but probably better than dino oil).
For dino oils, Delvac-1300 and Delo-400 are probably the best - Rotella is nothing special. Biggest thing is to make sure you are using diesel rated (CH, CH, CI, etc) oil! Very few 20W-50 oils are diesel rated, and not all that many 10W-40's or straight 30's are either. This is the most important item - if it's not Cx rated, it can't suspend the soot properly, and you'll get excessive engine wear.
For the record, I use Delvac-1 and very strongly support using full-synthetic oils in almost all vehicles, with extended drain intervals, based on the results of oil analysis (which is 10-15kmi for my cars).
YMMV, etc. Now can we close this thread before it swells into a 10-page oil war like all the previous threads did?
