Ford 1S7Z-8575-AG Thermostat Assembly

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Start by checking the coolant level, drivebelt tension, and temperature gauge operation.

Before starting the removal process, disconnect the battery negative cable and drain the cooling system if necessary. On specific engine models, remove the drive belt, power steering bracket and tube, and air conditioning compressor without disconnecting the hoses. Remove the cooling fan and shroud, and on Duratec models, remove the ignition coil cover. Release the hose clamps and twist the radiator hoses to remove them from the thermostat cover or housing. Loosen and remove the bolts from the thermostat cover or housing, and withdraw the thermostat while noting the position of the air bleed valve and how it is installed. Replace the thermostat rubber seal with a new one on installation. To test the thermostat, check if it is stuck open or closed, and heat it in cold water to observe when it begins to open. Ensure it opens and closes as specified; otherwise, replace it. During installation, clean the mating surfaces, replace the sealing ring, and fit the thermostat in the same position as before. Tighten the bolts to the specified torque setting, reconnect all coolant hoses, and refill the cooling system. Start the engine, allow it to reach normal operating temperature, and check for leaks and proper thermostat operation.

Before assuming the thermostat as the cause of a cooling system issue, perform preliminary checks including verifying the coolant level, drive belt tension, and temperature gauge operation. If the engine takes an unusually long time to warm up, possibly indicated by heater performance or temperature gauge behavior, a stuck-open thermostat may be the issue and should be replaced. In cases of engine overheating, assess the upper radiator hose temperature; if the hose remains cool while the engine overheats, a stuck-closed thermostat may be to blame, preventing coolant from escaping to the radiator. In such cases, replace the thermostat to resolve the problem. It's essential not to operate the vehicle without a thermostat to maintain proper computer operation and avoid adverse effects on emissions and fuel economy. To replace the thermostat, disconnect the negative battery cable, remove the air cleaner air duct if necessary, and drain the cooling system. Locate the thermostat housing by following the upper or lower radiator hose, and disconnect electrical connectors if present. For some engines, the thermostat and housing are serviced as a unit. Loosen and detach the hose from the fitting, and if necessary, cut off an old or deteriorated hose and replace it. Remove the housing cover bolts, detach the cover, and remove the old thermostat. Clean the housing and cover surfaces, ensuring a proper seal for the new gasket. Install the new thermostat with the correct orientation, replace the housing cover, and tighten the bolts to specified torque. Reattach the hose, refill the cooling system, reinstall the air cleaner air duct if removed, start the engine, and monitor coolant levels and thermostat operation while checking for leaks.