For old 2-strke Detroits it's mono-grade only. SAE 30 for reasonable temps and SAE 40 for hot country like AZ and TX. They will shear down any multi-grade in no time and you will loose the engine eventually.
Lots of DD2 folks and discussions here. Even some fleet operators. All agree, SAE mono HD only. All the Add Paks for the appropriate oils will do well.
Delo works well and has taken some 8V92's out to a million miles. This is one place where second guessing the experts is really not a good idea ...
Edited by BrocLuno (06/13/18 10:22 AM)
Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.