All about Ford Mondeo

Thermostat - removal, testing and refitting
Cooling, heating, and air conditioning systems / Thermostat - removal, testing and refitting

Note: Refer to the warnings given in Section 1 of this Chapter before starting work.

1 Disconnect the battery negative (earth) lead (see Chapter 5, Section 1).

2 Unbolt the resonator support bracket from the engine compartment front crossmember.

Slacken the two clamp screws securing the resonator to the air mass meter and plenum chamber hoses, then swing the resonator up clear of the thermostat housing (see Chapter 4).

3 Drain the cooling system (see Chapter 1). If the coolant is relatively new or in good condition, drain it into a clean container and re-use it.

4 Disconnect the expansion tank coolant hose and the radiator top hose from the thermostat housings water outlet.

5 Unbolt the water outlet and withdraw the thermostat (see illustration). Note the position of the air bleed valve, and how the thermostat is installed (which end is facing outwards).

4.5 Unbolt water outlet to withdraw thermostat
4.5 Unbolt water outlet to withdraw thermostat

General check
6 Before assuming the thermostat is to blame for a cooling system problem, check the coolant level, auxiliary drivebelt tension and condition (see Chapter 1) and temperature gauge operation.

7 If the engine seems to be taking a long time to warm up (based on heater output or temperature gauge operation), the thermostat is probably stuck open. Renew the thermostat.

8 If the engine runs hot, use your hand to check the temperature of the radiator top hose. If the hose isnt hot, but the engine is, the thermostat is probably stuck closed, preventing the coolant inside the engine from escaping to the radiator - renew the thermostat.

Caution: Dont drive the vehicle without a thermostat. The lack of a thermostat will slow warm-up time. The engine management systems ECU will then stay in warm-up mode for longer than necessary, causing emissions and fuel economy to suffer.

9 If the radiator top hose is hot, it means that the coolant is flowing and the thermostat is open. Consult the Fault diagnosis section at the front of this manual to assist in tracing possible cooling system faults.

Thermostat test
10 If the thermostat remains in the open position at room temperature, it is faulty, and must be renewed as a matter of course.

11 To test it fully, suspend the (closed) thermostat on a length of string in a container of cold water, with a thermometer beside it; ensure that neither touches the side of the container.

12 Heat the water, and check the temperature at which the thermostat begins to open; compare this value with that specified.

Continue to heat the water until the thermostat is fully open; the temperature at which this should happen is stamped in the units end. Remove the thermostat and allow it to cool down; check that it closes fully.

13 If the thermostat does not open and close as described, if it sticks in either position, or if it does not open at the specified temperature, it must be renewed.

14 Refitting is the reverse of the removal procedure. Clean the mating surfaces carefully, renew the thermostats sealing ring if it is worn or damaged, then refit the thermostat with its air bleed valve uppermost (see illustration). Tighten the water outlet bolts to the specified torque wrench setting.

4.14 Ensure thermostat is refitted as shown
4.14 Ensure thermostat is refitted as shown

15 Refill the cooling system (see Chapter 1).

16 Start the engine and allow it to reach normal operating temperature, then check for leaks and proper thermostat operation.

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