So update after a while. About a month ago I had a garage change the coolant and also the thermostat. For a few weeks everything worked fine, the heating, the engine getting to the right temperature in the right time, coolant not disappearing. But after a few weeks, four or so, driven about 1000 km, the coolant is one mark under the minimum mark. So it is leaking somewhere. I need to make a trip 800 km round trip next weekend so I am not sure if I can manage to get the leak sorted out before the trip. Can I just add some paraflu coolant to the tank so it is somewhere near the max mark? I suppose after this it will take a few weeks before I lose the coolant under the min mark again and it is not so expensive to add a litre or so of paraflu for once. Not sure if it is OK to add just paraflu or water or the right mix of both.