One thing to check, is there any evidence that coolant is being ejected/dumped out of the reservoir?
I thought that after I had initially changed the coolant in my 2011 Audi S4, I was being clever refilling the reservoir to the MAX instead of half way between the MAX and MIN, I was wrong, every time we stopped, after driving for maybe 100 miles, the next morning the level had dropped to a bit lower than half way between the MAX and MIN and I wrongly interpreted that to mean that more air was being dumped out of the system and so making room for more coolant - when in fact, I worked out that what was happening was that the remaining trapped air was expanding when the coolant was at normal operating temperature and so dumping some of the extra coolant I had put into it out through the top of the reservoir. As soon as I worked that out, I stopped refilling the reservoir and no more coolant got ejected/dumped out, though as I said earlier, I think that there is still air in the highest level of the system, ie in the supercharger heat exchanger, so that is what is still causing the coolant level to rise when the coolant is at normal operating temperature.
Getting rid of that is still a job to be done, having that air in there will only mean that if I ever thrashed that car, it would not maintain its rated max power output as the supercharger heat exchanger would not be cooling the incoming compressed air down to the correct level - but that will never be a
problem for me, though I will attempt to bleed the 2 heat exchangers as they will never self bleed by themselves as that coolant circuit is in a branch with its own pump and air to coolant section of the radiator.
