Ken,
The issue with waste motor oil is the very fine metal and other contaminates in it. The new Diesel engines are running very high injector pressure for a very fine spray and the metal and other crap in the WMO will cause erosion to the injectors and cause poor engine performance. That’s why Cummings use to say 15% WMO was ok. If you could remove all the crap from the WMO it would be ok to run it in a new Diesel engine.

Willbd