The thermostat must be replaced in the following order.
Remove the upper part of the air filter housing together with the air flow meter, the stiffening plate, the fan shroud and the fan drive coupling with the impeller.
Drain the coolant and dispose of it. Disconnect the cooling system hose and plug connector (10) from the thermostat housing.
Loosen the bolts (8) securing the thermostat housing cover and remove it together with the built-in thermostat. Check the operation of the thermostat.
Clean the mounting surfaces on the thermostat housing and coolant pump flange from dirt and traces of oil. Replace the sealing ring (7).
When installing the thermostat, tighten the cover mounting bolts to a torque of 10 N·m (1.0 kgf·m). Replace the sealing gasket and tighten the drain hole bolt (M14x1.5) on the cylinder block to a torque of 25 N·m (2.5 kgf·m).
Install the stiffening panel. Fill the engine cooling system, bleed the cooling system and check it for leaks. If leaks are detected, slightly tighten the mounting bolts.
Check the operation of the viscous coupling (turning on the fan), has the temperature at the bottom of the radiator increased and is the thermostat housing sealed?.