The Zetec is a dual-overhead cam, or DOHC, four-cylinder engine manufactured by the Ford Motor Company and used in some of its small cars, such as the Focus and Fiesta. The Zetec's thermostat regulates the temperature of the cooling system. The thermostat stays closed when the engine temperature is low, then opens when the engine reaches operating temperature. A faulty thermostat may cause the engine to overheat, necessitating its removal for repair or replacement.
Open the bonnet of the vehicle and allow the engine to cool down completely before beginning this procedure.
Place a drain pan under the radiator. Open the radiator drain valve with a wrench and allow the coolant to drain into the pan. Close valve when the coolant has finished draining. Slide the drain pan from under the front of the vehicle. Save the coolant, if desired, to pour back into the radiator once the thermostat has been replaced.
Locate the EGR tube brackets on the driver's side of the engine near the air filter housing. Remove the retaining bolts from the bracket with a wrench, then push the EGR tube downwards slightly to create extra working room around the thermostat housing.
Squeeze the tabs together on the upper radiator hose clamp on the thermostat housing with a pair of pliers. Slide the clamp away from the thermostat housing. Grasp the hose and pull it straight off of the housing. Remove the rear hose from the thermostat housing in the same fashion.
Remove the three retaining bolts from the thermostat housing with a 10mm socket and a ratchet wrench. Push the thermostat housing up slightly to reveal two more smaller hoses attached to the underside of the housing. Remove the hose clamps and pull the hoses off the housing in the same fashion as the removal of the other two hoses.
Remove the thermostat housing from the engine bay. Remove the three retaining screws from the thermostat retaining ring on the housing with torx screwdriver. Remove the retaining ring, then lift the thermostat straight up and out of the housing.
The thermostat and housing can be installed by reversing the order of the above procedure.