His response was to use a quality name brand and change at regular intervals, yearly. He also said that some folks with the TT's run Redline's Water Wetter coolant aditive that breaks down the surface tension of the water so it has better heat transfer in the radiator. You can get it at [ www.myoilshop.com, ] they also have info about the product. I used it in a Mercedes in Fl and it did make a difference in temps.