Help! Coolant leak

[Zoe11]

hi,
I am hoping someone can help and give me some possible solutions or ideas.
I brought my 2003 Audi A3 18 months ago, ever since I had it I have had to top up the coolant every few weeks dependent on how many miles I have done. Over the last week it has become extreme and I am having to FILL UP the water bottle 1-2 times s day again Dependent on miles done, but it sometimes seems the water disappears over night too.
It has had a pressure test and the cannot find and external leaks, they have also done the head gasket gas test in water bottle which came back fine.
The car drives fine other than a starting issue sometimes which I don't know if related or not.

My car is 2003 Audi A3 tdi

Thanks, really hope someone can she's sone light on what I can get checked next without having to spend ££££ going direct to Audi

 

[Wil147]

Wow that is a lot of water it's losing!
If you cannot see any external leaks, and the carpets are dry inside the front are dry, make sure there's not a airlock in system, confirming this!
There's only 1 place it's going into the cylinder or into the oil, check you oil level and oil quality make sure it's not mixed
If it's going into the cylinder over night this could be causing hard to start, but this needs to be checked asap as it could
Hydraulic lock


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[8989james p]

Has it been pressure tested from cold? Water pump ok? Circulating? Check return pipe on coolant bottle. Thermostat ok. Not jammed closed. Feel pipes when at 90deg if pipe after thermostat r cool/luk warm then jammed closed.

 

[vag-tech]

All of the above. Could clamp cabin heater pipes to rule out.