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Testing Cooling Fan and Radiator Thermoswitch

Note that the electric cooling fan will operate only when the temperature is high enough to close the radiator thermoswitch or, on cars so equipped, the after-run thermoswitch. If a faulty thermostat is not allowing the coolant to bypass the radiator and warm up to the switching temperature, the thermoswitch will not close and the cooling fan will not run.

To test the cooling fan, disconnect the radiator thermoswitch connector and use a jumper wire (with switch) to make connection between terminals to simulate a closed switch. On three-terminal connectors used with two-speed fans, the fan should run at low speed when the red wire is jumpered to the red/white wire. It should run at high speed when the red wire is jumpered to the red/black wire. Thermoswitch location is shown in Fig. 4-9.


Always keep clear of the fan blades. The cooling fan may run at any time, even with the ignition off.

If the fan does not run, check for voltage at the thermoswitch connector. There should be battery voltage (approx. 12 V) at terminal no. 3 (red wire) whenever the battery is connected. If not, check fuse no.1 in the fuse/relay panel. For more information on the cooling fan circuit, see ELECTRICAL SYSTEM.

If the fan runs only when powered directly by the jumpered connector, the radiator thermoswitch should be replaced.

Fig. 4-9. Radiator and cooling fan used on 16-valve models. Other models are similar.

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