Join Date: Aug 2003
Location: Long Island, NY
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As mentioned, the 'normal' operating temperature depends on if the boat is cooled with engine coolant or salt water.
I am going to assume that you have a heat exchanger and that the engine is cooled with engine coolant. If that is the case, the engine *should* run at whatever temperature the thermostat opens. I feel that 180 is best to provide complete combustion while not overheating the oil.
My boat has a Universal M25 - a 21HP engine with heat exchanger. The thermostat is a 180 and the engine runs at 180 almost all the time. The boat is in the Long Island sound and the water is close to 80 degrees now. I can motor at 80% of max RPM and the temperature stays at 180. If I push to 90% of max RPM the temp may go up to 185 or 190. In the spring and fall, when the water in the sound is cooler, I can never get the engine over 180.
IMHO, if your engine regularly exceeds the thermostat temperature, you either have a problem with your cooling system (clogged heat exchanger, bad raw water pump), the cooling system is undersized (like early M25 engines with 2" HX) or maybe the sea water is really warm. What temperatures do Florida boats run at?
Deep Blue C, 2002 C&C 110
Mt. Sinai, NY
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Last edited by BarryL; 08-05-2010 at 10:35 AM.