Not coolant temp sensor ???

[markyc100]

Replaced my coolant temp sensor on my 2001 A4 1.8t and car is no different, i had a look at the housing where the thermostat is and where the sensor is housed the plastic has broke off that holds it in place so it's not secure, could this be causing it, any idea how much a new thermostat housing is, and is the sensor built in ??

 

[AndyMac]

You can tell if it's the thermostat from the symptoms. If it's stuck open the car will only crawl to 90 degrees when idling/stuck in traffic. If it's stuck shut then the car will overheat pretty much all the time. They normally get stuck open though.

 

[markyc100]

Does anyone know what the sensor on the thermostat housing is for, and would it affect the temp reading, also the fan seems to be on all the time, replaced the coolant temp sensor.

Thanks

 

[ScottyP45]

hi mate,

The thermostat itself acts independently from the car and is a thermo-mechanical device that simply regulates the flow of hot water into the radiator.

The sensor is to monitor the water temperature for the ecu.

If the sensor was pulled out of its socket it would read atmospheric temperature, which is obviously cool compared to engine water when hot, so this wouldnt make the fans come on, quite the opposite. Perhaps the ecu has cut-wire detection built in and if it can't "see" the sensor, puts the fans on as a precaution so the sensor is made fail-safe. Which might point to a wiring or connection fault between that sensor and the ecu.