Engine Overheat - Stuck Thermostat?

midexp

Active Member
Oct 5, 2016
423
Harrison Township, Michigan Lake St.Clair
Boat Info
1999 40' Sundancer
Engines
454 merc
Mercruiser 7.4L Horizons closed cooling. Starboard engine went to 180 yesterday. The coolant recovery bottle is filled to the top (was at the normal fill level prior) and I did not see any coolant in the heat exchanger when I open the cap. I'm guessing the thermostat is stuck and not allowing the coolant to flow through the heat exchanges? And if I replace the thermostat, will it draw the coolant up from the overflow bottle up to the heat exchanger, or will I need to add coolant to fill the heat exchanger?
 
Assuming all cooling system components are operating properly including the heat exchanger cap and the closed cooling system is sealed the closed cooling system will draw from the reservoir.
If the closed cooling system is significantly low start by topping off leaving room for expansion.
 

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