Thermostat, Engine Cooling
ThermostatIf the thermostat opening temperature is less than 88°C (190°F) on 5.4L engines or 82°C (180°F) on 6.8L engines, install a new coolant thermostat.
If the thermostat opening temperature is greater than 82°C (180°F), the coolant thermostat is good, a new thermostat should not be installed.