I ve done a fair bit of searching and the two usual culprits for dodgy temp readings are the coolant temperature sensor and the thermostat.
Audi q7 coolant temperature sensor location.
Genuine audi part 059919523a 059 919 523 a 059919523f.
Engine coolant temperature sensor.
I ve not got vcds yet but i hooked it up to my live obd2 box and the coolant temp being reported hovers around the 50 54 degrees mark.
The main one is that the coolant temperature gauge hardly moves.
The average cost for an audi q7 engine coolant temperature sensor replacement is between 128 and 190.
The coolant temperature sensor should be located very close to the water outlet from the engine if you follow the radiator top hose back to the engine and then look in the immediate area on the cylinder head you should find the 2 wire coolant sensor.
Here is a quick video on how to replace a temperature sensor on an audi a6 with a 2 8l engine.