[HoosierDaddy]

I cannot compare them directly. My old 1978 Newell had a Cummins. It ran fine ,no major expenses. My current 1993 Newell has a Detroit 8V92. It runs fine...No major expenses so far. Regardless of which engine you get the most important thing is preventative maintenance:
Oil
Filters-oil, air, coolant if needed, fuel.
radiator kept clean
Coolant should be maintained.
Each engine family has minor differences in ideal operating procedures but I don't see any major differences in maintenance costs.