I bought a 2006 audi a4 2.0 quattro from Halifax Monday and the heat worked so good I was sweating all the time getting pissed of until this morning thrusday February 24th where the heat barley works when I have it up to the windshield.... the only thing i did was add under a quarter bottle of that super cool, if used it In every single car I owened with no problem in Vw, Nissan a Saab and the last car I used it was a 2012 hyundai veloster where I had a full 2 bottles In it .... the heat gage is staying at half so not heater core. I guess it could be thermostat but it worked really good into this morning