Hi all, Here’s a summary of my coolant problem (I’ve had it for a few weeks): •Vehicle. Skoda Fabia TDI RS •Cool water evaporates regularly (every 50km) when the engine is warm (display 90°C) •Interior heating works quite normally; in the overflow tank (if you call it that?) I also see water being transported. So the water pump should work. •The heat exchanger of the large circuit always remains cold (I assume it should be in normal condition). And when driving on the motorway, you get so warm that you can feel it with your hand, right?) Ergo: big circuit is not flown through by the cooling water 1. Suspicion: Thermostat defective. I ordered and installed a new thermostat (was quite easy; LiMa doesn’t even have to be folded out, but just to the front. I could leave belts on it). Interim result: no change It is still the case that the large circuit is not flown through, even though the pump runs and the thermostat is new. first question: When changing thermostats, air was certainly also released into the system, and certainly also into the large circuit. I did not vent anything, since I assumed that the air would be transported through the circuit after a short time and that it would be stuck in the balancing tank and that it would be gone the next time. If that was the case, then my second suspicion: large circuit is clogged. Therefore, I think I could dismantle the heat exchanger and use tap water or Rinse through high pressure cleaners. Maybe even soak with correga tabs or something like that. I’ve also read that you give any cleaner directly into the cooling water. But if the large circuit is actually clogged, then nothing comes from the cleaner on the heat exchanger. Quite basic concerns or comments?