Note: You will need an ohmmeter to check for proper operation.
Examination
1. On the F8Q 620 engine, the sensor has two functions. The NTC resistor tells the heater control unit the coolant temperature, and the switch interrupts the power supply to the EGR solenoid valve. On the F8Q turbocharged and F9Q engines, the sensor has only one function - it tells the injection ECU the coolant temperature. In both cases, the sensor must first be removed as described below, and then it can be tested.
2. On the F8Q 620 engine, connect an ohmmeter to pins 1 and 4 of the sensor connector. At room temperature, the resistance should be infinite, i.e. the thermal switch contacts are open.
3. Then tie a string to the sensor and lower it into a container of water (it should not touch the walls or bottom of the container). Immerse the thermometer in water and begin heating it. Check that the contacts of the thermal switch remain open up to 20°C and close at 30°C. When the contacts are closed, the ohmmeter should show zero resistance.
4. On all engines, connect an ohmmeter to terminals 2 and 3 of the switch (the F9Q engine only has two terminals). Heat the water and check that the thermistor resistance (coolant temperature sensor) is in accordance with the data given in Specifications.
5. If the results obtained are not satisfactory, the switch is faulty and must be replaced.
Caution! Remove the temperature sensor only from a cold engine.
Removal
1. The sensor is attached to the thermostat housing, on the left side of the cylinder head. It has a black connector on the F8Q engine, or a white connector on the F8Q with turbocharger.
2. Drain the cooling system as described in Chapter Maintenance. Alternatively, have a new sensor or suitable plug available to quickly plug the hole and prevent fluid from leaking out.
3. Disconnect the connector, then unscrew the sensor. Remove the sealing ring.
Installation
1. Install in reverse order, use a new O-ring.
2. Finally, fill and bleed the cooling system as described in Chapter Maintenance.