Thanks to all for their interest and contributions. I believe Ivymike has come closest to the cause of the problem in this case. Smyptoms seem to be unique to applications running intercity delivery service on mountainous routes requiring frequent variations in engine speed and load. Oil...
I am concerned about where the loosened carbon might be lodged, potentially blocking oil passages in the turbocharger. Has experience shown this concern to not be valid? If the oil filter is in the by-pass mode, it is possible that oil supply from the pan is unfiltered.
In diesel engines carbon build up, leading to stuck piston rings, can be a problem. Is there a product that can be safely used to clean pistons and free stuck rings in a turbocharged, diesel engine, without removing the pistons from the engine? Commercial products appear to be limited to...
