Good news - I hope
 

My S8 was suffering from slow coolant loss for a while. I was prepared for the worst expecting oil cooler pipe leaking, even ordered the metal pipe to replace it.

I wanted to get this sorted before going to Scotland so on further investigation it revealed to other less intimidating faults:

1. Electric radiator fan has packed up reducing cooling power (new one already in the post)
2. Trying to find out the source of leak I blocked radiator and ran car on iddle to build up some temperature and pressure to make leak more intense. This resulted in expansion tank cap blowing fluid at around 100C. This should not happen until 2 BAR of pressure which should be in 120-130C region. Looks like the cap cannot hold the pressure so new one on will be ordered and hopefully will sort the problem as I definitely do not want to do oil cooler job.

It could be a LOT worse.

Great investigating 👍