If needs be i have a spare leak free expansion tank that you could have for free Andrew. The sensor in it is hit and miss but at least you would eliminate the leakage question.
Thank you
@Special edition Dave, that is extremely kind. As I had the coolant loss issue with the old expansion tank (Sep-2018), and the first items to be replaced trying to troubleshoot the issue were the expansion tank and cap (Feb-2019), I don’t think the issue lies there.
I need to try to understand why the pressure in the system is sufficient to push coolant out of the expansion tank pressure-relief valve, and yet the radiator fan has not kicked-in. As I have said several times, I don’t understand the mechanics of cars, but I am using the analogy of what is going on when I use my pressure cooker.
Using the pressure cooker I use maximum heat to get the contents up to pressure, indicated by the weight, then I reduce the heat to maintain temperature and pressure at an optimal level. If I turned-up the heat, the pressure-relief valve would open, there would be a big mess on the stove, but there wouldn’t be an explosion. This is a process in which I need to participate by managing the application of heat.
Back to the car. When I drive the car, and the temperature of the coolant increases to certain level, I would expect the radiator fan to spin to reduce the coolant temperature. This should be an automatic process requiring no input from me. If this doesn’t happen, temperature and pressure increases, and the expansion tank pressure-relief valve will spray coolant around the engine bay. I suspect this is what I am seeing, and I may have come to the limit of what I can observe.
I probably need to take it to a garage with VCDS and repeat what I did on Saturday. The question I need to answer is do I remain loyal to the local, excellent, VAG specialist, but with a new, and younger Audi Master Tech who may not have seen too many A2s; or do I travel to WOM who I know have an excellent reputation and a growing band of loyal A2 customers, and so really know their way around these cars.
Cheers, Andrew