Fit a Water Temperature Gauge

[rastiazul]

The easiest way to check this is to warm the motor with a short drive, leaving the engine running, park up & put the heater controls to "off' (cold). After a short period of time the temperature of the coolant will rise enough to make the sensor switch the fan on. The fan will then turn itself OFF as the temperature of the coolant drops. This cycle should allow the engine to perform quite happily on tick-over.

After how long should the fan turn itself off? After going coming from a short ride I left the car on for 20 minutes and it didn't turn off

 

[André4Renaults]

It appears that your car's cooling system may have an air lock somewhere. Once warm, the sensor will become hot enough to turn the fan ON, which will cool the water in the radiator. As this cooler water passes through the pipes it reaches the sensor, which becomes cooler, and it turns the fan OFF. This process repeats itself, but how quickly it does so depends on the engine speed, the pressure of the coolant and the overall efficiency of the cooling system. An air lock would prevent the cooler water reaching the sensor, but that might not be the cause of your fan continuing to run for a long time.

 

[rastiazul]

Thank you
I just read somewhere that the fan in my '74 "functions constantly" . So I guess it doesn't turn off