hi just wanted to share my experience as it may help someone. My problem got worst over course of a year and it was very frustrating as even a independent Audi garage struggled. My car is early 2012 a7 3.0t fsi CGWB similar to s4/s5 engine with just under 60,000 miles. First symptom was coolant temp gauge went up rapidly with normal driving and went into the red zone alerting me to stop the car. After some time the coolant gauge went to the middle again. This happened over several months and was very frustrating as no fault codes and the problem NEVER happened while in the garage. There was even times I didn’t want the car back as the problem can be worrying on a long drive. Eventually the garage suggested to replace thermostat however £400 odd later the problem was still there. I managed to stop the car and open the bonnet while it was overheating once and the radiator top hose was fairly cold including the expansion tank. So I got around to replace the coolant temperature sensor on the front of the engine. Problem was actually still there but I also noticed when sitting at idle the coolant temp would sometimes drop to one bar on a warmed up engine. Again and again the problem would happen but not always it was intermittent. Eventually a coolant system failure warning came up while overheating (took best part of 10 months) and the garage read the fault code...coolant pump mechanical failure. So the car was booked in for the repair. Just before it went in I did a little more research as the water pump failure didn’t explain the overcooling at idle. I came across a guy on Aeuromotive forum who went through two water pumps and two thermostats to still have the problem. And he got further help and an Audi garage diagnosed the fault as faulty coolant control solenoid (n489) valve. I asked the garage to test the water pump and solenoid (which supplies vacuum to the flow controlled waterpump so the impeller can pump more or less coolant). Also the n489 is also responsible for allowing the engine to warm up quicker which would explain the rapid overheating. The garage tested both of these items and they were faulty so another £400 later the problem looks like it is fixed! The sleeve that moves up over the impeller to slow down coolant flow was getting jammed. The garage thinks the overuse of the waterpump caused the n489 solenoid to wear out. Picture to follow I could have fixed the problem from the beginning by just replacing the waterpump and solenoid at £400 odd instead of the £900 I spent also doing the thermostat and temp sensor but at least I done some preventative maintenance . Car shouldn’t be holding back on any power now and should be little more eco as waterpump can work properly.