I was told over two years ago that because my heater wasnt getting overly warm and the car was losing a bit of water that my head gasket was probably on its way out..... 20k later and we are still on the same head gasket, the heater gets a little warmer as the car's now in daily use, but when I put the heater blowers on full, it cools down again. It still loses a bit of water but I aint worrying.