9I completely understand. I am aware that you work, and that you are giving your advice for free, and I appreciate it. My partner and I also have busy lives, so my replies can't always be immediate. I have only asked for advice to see if there is anything we can do to get our money back from this unhelpful garage.
There is nothing my partner could tell you different to that which I've already said, and he is not in a position to be able to navigate around the technicalities of using a forum, understanding the legal terms and putting together a case. So it's down to me, and I am autistic with a side helping of ADHD so there are times when my executive functioning gets so poor that I cannot even think about working on this issue.
Our friend, who is the mechanic, is also super busy, he has kindly given us his time for free to help sort out the issues with the car and write his report, which I have given below. So far as I have been able to, I have answered all your questions also below.
Amount paid - £5999
Method of payment - Visa Debit card
Vehicle model - 2015 Skoda Octavia Elegance 1.6 diesel
Mileage (as of 4/3/2022) - 125,413
Report from mechanic -
Investigate coolant loss :- fore note.. coolant loss amount is approximately an expansion bottle in 4 days over 50 miles of use.
Removed upper and lower engine covers(including upper timing belt cover),raise car and pressurised coolant system to approx 10 psi (engine cold) visually check all areas of coolant system.. hoses, radiator/ heater matrix,water pump,
No visible leak..run engine to running temperature with applying pressure and releasing to apply different conditions and no leak visible.
Carried out a carbon monoxide (exhaust gas sniffer) test at expansion bottle again a cold engine through to operating temperature, finding no gases present in cooling system which in turn eliminates head gasket/cracking near combustion area's and EGR cooler... only leaving 2 components left ,inlet manifold heater/cooler...and throttle valve (both have coolant passing through)
Make and fit a temporary bypass pipe for the intake manifold and car driven for the normal conditions of coolant loss and found over a 3 week period no coolant was lost.
In findings the possibility of the coolant being drawn in to manifold between turbo boost in the manifold and depression on overrun/decceleration .
We do not yet have any costs for how much it will cost to have the repair done, this is currently work on progress.