I've had my Superb a couple of months now. TDI CR170 DSG estate Elegance.

 

Ever since I got it, it never got up to temperature. Even after 20+ miles at 60mph, the temperature gauge never got over 70 degrees. 

In town it would eventually creep up towards 90, but as soon as I was doing anything more than 40, it would start dropping back down again.

 

I took it to a local garage who had the car for a few hours to diagnose. They diagnosed a stuck main thermosat, as the pipes were the same temp either side of the thermostat, even well before the car was up to temperature.

The car is under warranty, and the used car dealer that I bought it from have paid for the work without any quibbles, as the garage had diagnosed it as faulty.

 

This work was done last week, but even after changing the main thermostat, it's still not much better.

 

If I am just driving normally on 60 roads, with air outside at 15c, after 15 miles or so the gauge isn't much above 60.

Thrashing the car, it rises up and does reach 90.

 

As soon as you let off and drive sedately again, it starts falling back down.

 

After looking on here, I'm guessing the culprit is the thermostat for the DSG cooler - but how do I categorically prove it is?

Understandably the dealer I bought it from doesn't just want to throw parts at it.

 

I could just buy it and fit it myself, but as it's under warranty, it's not something that I really want to be doing.

To @softscoop - 99% of this Problem was caused by faulty "DSG"-Thermostat. Change it without doubt

+1 for DSG thermostat. It's about €35 from a dealer for the part. You'll need some coolant to top up the system after changing it.

Plus 2 for the DSG stat. Plenty of topics including one I did after reading others. Very easy DIY job. I got a Mahle part from Autodoc at the time. Do a search you should find my posts and loads of others. Someone did pictures and instructions also.