I had my 40K service done and the shop told me that while my coolant tested to -35ºF the pH was at 7. The shop guy advised a coolant flush saying that the coolant starts out as alkaline and shouldn't go acidic and since my coolant has gone from alkaline to neutral, I should change coolant before it goes acidic. Now, I've read that coolant pH should be in the range of 8.3 to 10.5 -- that 6.0 to 7.5 is too low and above 11 is too high. I haven't found anything about VW's G13 coolant. I called another independent VW/Audi shop, referred to me by a trusted friend, and that guy told me not to worry and change the coolant if I need work done (i.e. water pump) or when I get to 80K miles. Does any of this make sense? Who do I believe?