Ford F5OY-8575-A Thermostat

You should check the coolant level, Serpentine Belt tension, and temperature gauge (or light) operation before diagnosing a faulty thermostat. If your engine takes too long to warm up, this means there is a stuck open thermostat that has to be replaced. When an upper radiator hose remains cool while the engine runs hot then it is very likely that its thermostat is stuck closed hence it needs replacement. When you feel a hot upper radiator hose it means that the thermostat is open so you need to find out the reasons behind the engine heat-up. Overheating results in serious problems such as head gasket leaks, scuffed pistons as well as warped or cracked cylinder heads. You should drain the coolant, remove the distributor cap (if necessary), disconnect hoses, remove the housing cover, extract the old thermostat, clean surfaces, apply sealant or insert O-ring seal, install a new thermostat, attach cover, tighten bolts, reconnect hoses (if they have been disconnected), refill coolant and check for leaks when replacing the thermostat.