Hi all. I have a 1998 afn engined a4 1.9 tdi. Recently it's started losing water and I can't find a leak. I have to top up the coolant everyday. During my journey the heater doesn't get very warm and after a while will suddenly blow stone cold at which point the engine temp starts to rise above the half way mark where it normally sits on the gauge. It seems dependant on how I drive. Once the heater blows cold if I drive it hard the temp rises. If I back off and take it steady the temp falls back to the half way mark. It's had a brand new thermostat and water pump only a couple of months ago. Is there a special technique for bleeding the coolant system or does this sound more sinister like head gasket failure?
Thanks in advance