HI Alan.
Im glad you posted this question. I have a 2002 A6 with A 2.0ltr fsi Alt engine fitted and also needs a thermostat changing. I have not had the chance to look at things yet. I also notice there is no haynes for the A6. May invest in the A4 one if it covers the ALT engine. The last time i went under the car to change the oil filter im sure the thermostat housing is in the same location. Its tight but im sure it can be changed from underneath. Also where would i find the air drain point on this cooling system. Somewhere on the top hose i have been told but cannot see it.
Darren Woods, March 2011