Coolant Temperature Sensor behaving backwards

[MercNJ]

Hi all, I have a 2008 Mountaineer 4.0L V6. The coolant temperature sensor seems to be behaving backwards. The temperature gauge on the dashboard seems to behave normally, but the electronic fan clutch does not. The fan clutch seems to be engaging when the coolant temperature is cool and disengages when the coolant is hot. Any ideas what could be causing this? This engine has the single temperature sensor in the thermostat housing. I have replaced the plastic thermostat housing multiple times over the years and more recently replaced it with an aftermarket aluminum one that seems to be much better. After all of these thermostat housing swaps, I may have lost track of the temperature sensor and not sure when it got replaced. Is there more than one type and could that be the cause?

 

[bluesq]

May be more than a coincidence...check my thread here: Service RSC Now + Code P0117

Did you use the Dorman aluminum thermostat housing? If so it uses a TX87 (screw in type) coolant temperature sensor. I have another one ordered up and I'm going to see if that fixes the issue.

The problem may be that the sensor is failing intermittently, thus the engine fan kicks on because it's not getting the correct reading. Then when it works again it shows the correct temp and the fan turns off because the system is aware of the temp and it is in normal range. You should be getting a check engine light if this is the case.

Not sure if that's what's going on with yours but it does sound really familiar...aluminum thermostat housing, fan kicking on, etc. Keep an eye on your temp gauge and see if it goes from normal temp to under C and back again when the ignition is on.