Engine Cooling Fan: Testing: Notes
Visually inspect thermostat for corrosion and proper sealing. If this is satisfactory, suspend thermostat and a thermometer in a container of water. Do not allow either thermostat or thermometer to touch bottom of container as this concentration of heat could cause an incorrect reading. Heat water until thermostat just begins to open. If thermostat does not open, replace.
NOTE:
Thermostat should open as water is heated.