102: Coolant Thermistor
Quick unit to complete depending on where your thermistor is located, in the case of the 2004 Mondeo it’s behind and underneath the ignition module on the water block expansion shown above plugged in on the orange and white wires.
Unplug from the harness.
A 20mm deep socket should see it off. From here you can either let your coolant/water drain out into a suitable container or you might want to consider draining the lot before hand and then renew the coolant/water to finish (in the real world). The truth is at college they are not going to let us drain coolant and put in new pre-mixes of coolant/antifreeze etc.. because it would cost money, they all just run on water and it’s not a big deal as these “college cars” will never go back on the road.
Next comes testing the thermistor. This requires taking an ambient temperature and then simply doing a resistance test on the thermistor to see what it gives us. The workshop was 11.1*C today and following this with the multi-meter we got 042.1 ohms.
So this was the first resistance test done, now we had to test it when operating at 90*C so it was time to dunk the thermistor into something hot !
Boiling up some water I got it to 95*C on the gas hob which seemed reasonable.
These are pretty ideal to avoid getting burnt.
The resistance check came up quite different, here you can see a reading now of 2.454 ohms. From these findings of getting two widely spread readings it’s clear to see the thermistor is functioning correctly.
Upon refit I was advised to use copper grease on the thermistors thread.
We raised the car up afterwards to clean up this bit of water spill. To end the task we ran the car and checked the temp gauge. Apart from a few tech data entries for the task sheet that is the thermistor unit done.