A4 1.9 Tdi Coolant Loss

Please can somebody help me.
If I leave my '99 A4 1.9 Tdi (110) parked for a few days, the coolant level falls to well below minimum. It doesn't happen if I drive car the car every
day.
I suspected the obvious, a leak, but when releasing the cap there is a rush of air (in/out?). I assume if there were a leak, the internal air pressure would be the same as outside.
There is evidence of water escaping from the overflow, (white marks on looms below). I wondered if it were head gasket going and pressurising water, but there is no oil / water transfer.
Temp is normal on driving.
Cheers in advance,
Chris
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Hi Chris Could be a problem with the cap...maybe the relief valve in the cap is faulty. If the cap is ok you need to get your cooling system pressure tested Hope this helps
yoda

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rush
looms
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