QuickSilver Replacement Thermostat - Boat Replacement Thermostat 864493 - Boat Easy to replace with common tools. See your owner's manual for removal of non-functioning Thermostat and replacement of new thermostat. 170 F Degree thermostat. Produced by Mercury marine to our stringent original equipment Manufacturer specifications to maximize the performance of your Mercury and Mariner outboard or mercruiser stern drive