To replace a MerCruiser Alpha thermostat, first open the engine cover and locate the housing by following four houses to the appropriate box. Then open the housing and remove the gasket. Make note of the notch and valve positioning during removal, and then replacing the thermostat with a new part.
MerCruiser Alpha thermostats are kept within a housing that is attached to four hoses via hose clamps. This housing must be opened to access the gasket by removing the two bolts securing the housing to the engine.
Once you have access to the gasket, remove it. Make note of the indexing notch and wobble valve so the new thermostat can be placed in correctly in a later step. Use a pair of pliers to remove the old thermostat carefully, and discard the thermostat as it cannot be used anymore.
Position the new thermostat in the opening, paying attention to the indexing notch and wobble valve configuration. Double check the positioning, otherwise the thermostat may not function properly. Install a new gasket over this, and align the housing cover with all of the parts. Make sure to pay attention to the vehicle's manual when tightening the bolts for the housing, to avoid overdoing the torque.