tempremental coolant needle

[gtiboy]

Had a problem with the coolant temperature needle not moving so on recomendation changed the coolant temperature sensor with a genuine green on from TPS.
Topped the fluids after fitment and hey presto the needle moved and stayed at the recomended 90 degrees.
However now when i have the climate control on it dropps down to the minimum and when i switch it off it rises to the magical mark?
I have topped up the fluid and also flushed the coolant out (only g12 nbeing used )
The climate works as it should when asked ????
Just a little confused .

 

[Chrisw4266]

Explain climate control on do you mean the fan if so which speed or just when the temp display is on.

 

[gtiboy]

Its only when its on eg the temp is cool or warm .
eg. If i press the off button then the temp needle come to 90 if i then switch it on it starts to drop???

 

[mondo]

Its only when its on eg the temp is cool or warm .
eg. If i press the off button then the temp needle come to 90 if i then switch it on it starts to drop???

Did you get to the bottom of this problem, gtiboy ? i noticed mine do the same today only did'nt tie it in with the climate control

 

[gtiboy]

No pal its still the same.
I did a 450 mile journey over the easter bank holiday and had no problems apart from the coolant needle not behaving .
Just switched the aircon off and the needle moved to 90 switched it on and it came down ????
However on a long journey it stays about a third of the way on the dash display so i don't know .
If i have the climate control on 20 the needle hovers at about a third .

 

[kite]

Failed thermostat maybe..

 

[gtiboy]

Could be but why does it work when the air con is off .
Doesn't failed mean not working ?
The belts and pump etc have all been done before i got the car, i have done about 2000k in it since the belts etc were done .
I am in the process of working out the mileage returned on a full tank to see if that has been affected .
From a full tank i got 567 miles thats motorway and town. I was a little dissapointed to be honest but on advice (adams24)i have filled it back up and put a litre of 2 stroke oil in the tank also .
The car runs a lot smother and seems to be giving me better milage after a day of use so we will see.

 

[TED7]

+1 for failed thermostat.

Mines gone (stuck open) and if I drive anywhere at a moderate pace, the temp drops to minimum. If i'm stationary, it goes back to 90 while there is no air flowing through the radiator. Presumably yours is stuck partially open, hence not dropping to minimum, your climate control being on is causing either the heat to be dumped into your cabin on warm or the radiator fan is coming on to cool the air con radiator on cold.

 

[mondo]

I like your way of thinking here chaps. suppose for the price of a thermostat its worth a punt at the weekend.
let you know how it goes.

 

[mondo]

But after some thought, the time it takes to register the temp change dose seem to be a bit quick for the engine to be actually changing temperature. unless of course they make these audi things with very efficient cooling systems ??

 

[gtiboy]

On a a6 2.5 tdi its a front off and timing belt water pump etc etc to change the thermostat?
Or isnt it ?

 

[gtiboy]

On another note if the thermostat was open would i not get appalling economy?
I have just been on a 400 mile motorway journey with about 90 miles of town driving .
i filled up before i left and got 479 miles before the low fuel warning came on .
I was a little dissapointed but on research its quite good apparently????
I have a 2.5tdi quattro sport a6 avant

 

[wesmaster]

On another note if the thermostat was open would i not get appalling economy?
I have just been on a 400 mile motorway journey with about 90 miles of town driving .
i filled up before i left and got 479 miles before the low fuel warning came on .
I was a little dissapointed but on research its quite good apparently????
I have a 2.5tdi quattro sport a6 avant

I'd say that is pretty good mpg for an a6 q. But they do suffer from thermostats. Get in touch with Adamss24. He's the v6 tdi God.
But to me sounds like thermostat. What is your oil temp by the way? Mine goes upto about 100* and coolant sits at 90.
Or check your live data to see what the ecu is seeing from temp sensor.
Regards.
Wes

 

[mondo]

On a a6 2.5 tdi its a front off and timing belt water pump etc etc to change the thermostat?
Or isnt it ?

After more reading it looks like your right.
Kinnell they've just been done on mine, fortunately by the previous owner
Even more fortunate Adamss24 Hails from North London !

 

[gtiboy]

So assuming mine is stuck half open ?
What effects will this have on the car ?
I always thought worse mileage figures and car not runing right ?
But mine is running fine.
However i will in may be changing the belts and thermostate just for peace of mind in may.
Adams will be in line for that job.
If the car is runing right i dont know weather to bother .

 

[TED7]

I would presume if the temperature is low enough, the ecu will compensate by running rich, which may or may not leave unburnt fuel on your catalyst. Which will damage it (or them) over time.

Note - I'm making these assumptions based on my understanding of petrol engines. I assume a diesel will act in the same way.

 

[gtiboy]

Changed the coolant sensor again with another and the temp is running right once again.
The part supplied from TPS must have been faulty ?
Thanks for all your answers and tips