Hi guys. I have an Audi Q3 2016. I’ve had it almost 4 year and don’t plan on selling anytime soon. I have this stupid little issue that’s been ongoing for a year now. It’s a small coolant leak that my garage mate cannot find. Times I get in the car and it’s at red and tells me to switch off. I then go into the engine and open the bottle and hey ho the water appears. Then a week later I need to top it up. I’ve changed the water pump checked the oil. Checked the head gasket. Car drives minted and still we can’t find this leak. The fan comes on time to time. The now I didn’t drive the car Xmas eve and got in for a drive on Xmas day and again tells me to switch off. Which I’ve done and checked it again. And hey ho it’s low again so I top it back up. Oil is fine and so is everywhere else. I just can’t find this leak. I’ve now booked it into Audi they’re asking for £170 for a diagnostic. I just want this leak found and sorted. Any pointers. 

Could it be an air pocket Instead? 

Issue with the heater matrix or thermostat?