Check the coolant sensor circuit

I wondered if the coolant sensor was working. I wanted to test to see when the radiator fans would cut in.
You can disconnect the sensor and start the engine, then the fans will run - but what about the fan cut in?

If you have a multimeter you can check the resistance of the sensor which has a resistance of around 2.8K at 20 degrees. As the engine warms up the resistance drops. At 80 degrees it is around 270 ish ohms.

If you have a variable resistor or a resistance box then you can connect this to the disconnected sensor leads and vary the resistance, simulating engine heating. I used a resistance box and found that the radiator fans kicked in when I reduced the resistance to around 100 ohms.

As you reduce the resistance you will hear the engine speed change as there is a feedback between the temperature and the timing - effectively testing out that this feedback is also working.