1 If the coolant system contains lots of silt and corrosion, then it’s a good idea to extract the thermostat and clean it and its housing. Start by detaching any pipework that’s secured to it.
2 Undo the nuts or bolts that secure the thermostat housing in position. These may be difficult to undo and in some cases, the studs or bolts could shear, so spray over them with penetrating fluid.
3 Once you can remove or open up the thermostat housing, you will be able to see the thermostat inside. Extract it and then clean inside the housing. When refitting the thermostat and housing, fit a new gasket.