I still don't think that really good comparisons can be made between over the road (OTR) and marine engines, except maybe at idle. A diesel genset running in a low load condtion would replicate the battery charging conditions described quite closely. Conversations with the engineering staff at Cummins marine group here in Charleston would seem to support my conclusions.
Trying to compare OTR and marine engines under load isn't easy. The OTR diesel engine is usually operating at a much lower load for a given rpm than a marine diesel or generator engine. They also typically operate well below their maximum rpm. For an OTR engine to be placed under the same load conditions as a marine or generator engine it would need to be on a never ending uphill grade and operating at about 80% of it's maximim design rpm. These are the types of loads that a marine (crusing at or near hull speed) engine operates under. It is very simaler to a genset running under full load.
Carbon builup in marine engines is most often caused by high fuel schedues and low rpm, but can be reduced by ensuring that the engine is not running below it's design temp.
Moisture is a concern, but as long as the engine is brought to full operating temperature before shutdown it usaully is not a problem. Short run cycles that do not reach full operation are usually the primary cause of excessive condensation inside an engine.
The most common
cause of engine failure is overheating. Overheating by itself doesn't usually do the damage. It causes a loss of lubrication by breaking down the oil flim between bearing surfaces. I would rather have an oil temp gauge than a watertemp gauge if choosing between the two.
The point that I was really trying to make is that the opreatiing temperature of an engine (hot or cold for coolant and
oil) at a specific load and rpm has a tremendous impact on engine longevity.
Just my .02