Originally Posted by SeaHorse II
You mentioned that the coolant temp rises to 190 and stays there. Mine rises to 192 and stays there because the thermostat is wide open and won't cool any farther. (So says the Cummins people) At first this alarmed me but the specs allow the temp to go to 203 safely. They also said that the newer diesels (most..not all) run hotter to achieve a more complete burn. ( I know other people that have the same model engine that I have and theirs run at 180.) So it's tough to sort out the BS from fact.
I don't think there is much BS involved. When the t-stat is wide open at a given rpm you have as much flow as you can get and the rate of heat transfer is limited by the area of the heat exchanger and the delta-T of the seawater and coolant.
If MB ran in high sea temps his max temp might be higher if it is already wide open. Or his T-stat might open more and maintain the same temp ... up to some as yet unknown sea temperature.
Probably few boats, even with the same engines, achieve the same flow rates and heat transfer capacity as another make or model or even the same. A few degrees either way falls into the noise level.