Help Audi TT MK1 225 false overheating !!! Drive me insane.

[Fixanything]

Ok

Very randomly temp gauge goes hard right in to Red zone and 49c reads 121C ! Stop for a minute or so temp back down to normal and may not go red again for weeks of driving.

Changed thermostat X 2
Changed temp sensor green x 2
Pump and belt changed about 30k ago, checked impeller not spinning via thermostat hole.
Fan thermostatic control switch changed X 2
Fan relay control module changed X 1
Header tank sensors cleaned.
Fans both working hi and low speeds.
Everything appears to be working correctly.
Never looses any coolant.
OBDII ECT follows 49c maybe a few degrees different.
Does not seem to actually overheat however, very difficult to check because so random.

Please help, thanks
Mark

[Dr G]

Dash cluster been rebuilt? Temperature gauge going mental was always one of the key signs of failure.

Try here:

https://cartronix.co.uk/product/audi-tt-speedomete...

[Fixanything]

Would a dash problem cause 49c and OBDII temp to go to 121C ?

The dash has not been refurbished or replaced, it does have some display pixels missing, but useable.

Cheers
Mark

[justinio]

Fixanything said:

Would a dash problem cause 49c and OBDII temp to go to 121C ?

The dash has not been refurbished or replaced, it does have some display pixels missing, but useable.

Cheers
Mark

Sounds like dash cluster failure to me, especially if some of the pixels have gone.

[Blackpuddin]

Put some of this on the gauge:

[Fixanything]

justinio said:

Sounds like dash cluster failure to me, especially if some of the pixels have gone.

You think a pixel or two not working would cause 49c to go to 121C ! I'll be very surprised.

[Dr G]

You'd said previously it wasn't actually overheating; if the coolant is getting up to 121 then it is

If there are no obvious signs of overheating (head gasket, oil/coolant contamination etc.) then you'll want to manually measure temperatures (not gauge or OBD readings).

If the actual temperatures are in order then go back to the gauge cluster.

If not then I can't point you to anything that's going to solve it in 5 minutes. It could be a blockage, corrosion, inefficient radiator, wiring fault, ECU fault...

[Fixanything]

Dr G said:

You'd said previously it wasn't actually overheating; if the coolant is getting up to 121 then it is

If there are no obvious signs of overheating (head gasket, oil/coolant contamination etc.) then you'll want to manually measure temperatures (not gauge or OBD readings).

If the actual temperatures are in order then go back to the gauge cluster.

If not then I can't point you to anything that's going to solve it in 5 minutes. It could be a blockage, corrosion, inefficient radiator, wiring fault, ECU fault...

Dr G,

Thank you, although temp indicators are advising 121C I don't think it is however, I have tried to measure actual engine coolant temp at the thermostat housing with IR laser thermometer when it occurs but it's so random it has not proven possible to date !

[justinio]

Fixanything said:

You think a pixel or two not working would cause 49c to go to 121C ! I'll be very surprised.

You said it wasnt overheating, but the gauge was reading 121c. Therefore, faulty gauge.

Pixel failure is just an indicator of a faulty cluster.