Help please temp guage

[Martyj200]

HI all
I have changed my thermostat when having my temp gauge only reaching 70 (i got the thermostat from GSF car parts)
Temp seemed fine for a while then started playing up again, i have since replaced the rear temp sensor and things were fine for a little while again ( temp sensor also from GSF)
I have just this week bought and fitted audi genuine thermostat and temp sensor and if i have my heating off the temp will get to 90
when i turn the heating on it starts dropping???
any suggestions folks?
thanks
Martin

[markoA4]

whats the flow of coolant like. it could be an air lock. also i know this might sound silly but another change of temp sensor might as they can be faulty. i took me 3 sensors before it worked.

[Martyj200]

whats the flow of coolant like. it could be an air lock. also i know this might sound silly but another change of temp sensor might as they can be faulty. i took me 3 sensors before it worked.

I have just been out for a drive and have noticed....
when temp gauge is sitting at 90 and i turn the heater on hot, the temp gauge starts dropping.
If i then turn it to cold it starts creeping back up to 90.
and its also stays at 90 if the heater unit is off.
the hot air blower blows hot air and doesnt take too long from start up to blow good hot air.
it seems as though the temp gauge will only go funny when hot air is blowing???????????

[fourringsrus]

With ref to your sensor, the sensor for the temp gauge is the one in the bottom rad hose whereas the rear temp sensor is for the ECU and thermostat controls

[Martyj200]

do you think it might be the sensor at the bottom of rad house?

[fourringsrus]

I dont know which engine you have but in my A4 1.8t b6 the cts in the bottom rad hose is for cooling fans control and gauge, whereas the combination of that one working correctly and the one on the rear of the cylinder head working correctly , will then send info to the ECU which will instruct the electronically controlled stat ( if fitted ) and other functions like fuel mix etc

[sbt]

i thought the temp sensor at the back of the engine had 4 pins 2 for the temp gauge and 2 for the ECU the one in the bottom of the rad is for the fan

[pauldazzle]

i thought the temp sensor at the back of the engine had 4 pins 2 for the temp gauge and 2 for the ECU the one in the bottom of the rad is for the fan

Correct.