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Maybe it’s all car forums nowadays but Audi ones don’t seem especially helpful so figured I may as well pop back & try the VxON collective.... My car knowledge stops at a service or maybe changing my brake pads/discs.

Audi Q5 2009 Tdi 2Litre. Solid reliable workhorse.
205,000 miles on it but I service it 4-5 times a year.
“Mystery” coolant loss.
  • Doesn’t happen at idle.
  • Doesn’t seem to happen when left with weight on pedal to keep revs c. 2000.
  • When drive for more than 30 mins and it’s up to temp – loses coolant. About 1 litre in that period.
  • It is coming out in engine bay near the expansion tank.
  • Oil cooler was suspected but has since been replaced.
  • Expansion/header bottle itself has also been suspected and replaced.
  • Same with the pressure cap of expansion tank.
It does seem that “extra” pressure in the system is causing a release around the expansion tank – letting out pressure and coolant with it. ?? I don’t really know what am talking about here, clutching at straws a bit – hoping it’s not some micro crack in the head that has been missed. (If it is – it doesn’t seem to be coolant to oil. There are no signs of that – barring coolant going somewhere, and it seems to be coming out near the expansion tank).

The back story to this is a complete engine rebuild – but that itself seems to be fine...
Due to personal matters I took my eye off car service work ball in 2021 and water pump was missed – so it failed end of October 2021 took out cambelt etc.
Damage was minimal and as I had just had clutch and DMF replaced, opted to repair. Head and bits sent off to Redmans Precision Engine Centre...
That was all reworked, new cams, rockers arms etc
All put back together. Although there had been various delays – got vehicle on road end March 2022. Used it for work couple of times putting maybe 500 miles on it – then this mystery coolant loss started.

I have been using my 'nice' (ish) car for work and it has taken a beating in the last 5-6 months - wanting to get Audi back working or scrap and move on.....
 

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Morning
Please accept my apologies if you’ve tried all of the following iam not a mechanic and I am not trying to be clever
Are you happy new water pump is working ie moving water round ( it’s not an electric one and loose connectors etc)
A mechanic friend of mine once told me a tale about the only way to bleed certain BMWs was to jack up the front of the car so the radiator cap was higher than the engine block have you Googled your car you tube might have the answer
And finally have you tried ringing an Audi specialist they might say they all do that have you used such and such bleed screw which is hidden
Hope you get sorted nothing worse than this type of issue
 
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