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The thermostat on a 3.7 is on the inlet side of the cooling system. If you follow the lower radiator hose back to the engine you will find the black plastic thermostat housing. The thermostat housing is held to the timing cover with two 8mm bolts. Replacing the thermostat involves removing the bottom hose (if you want to), removing the two 8mm bolts that hold the housing to the timing cover, and removing the housing. The thermostat will stay captured in the housing, just pull it out of the housing.
When you refill the cooling system you will need to open the bleeder screw. If you follow the top radiator hose back to the engine you will see a 5/16" allen plug in the timing cover not far from where the hose attaches. This is the bleeder screw and must be removed when refilling the system.