Help constantly lacks cooling fluid..

Hello everyone, we are soon desperate here. Our Volvo V40 T Di Bj. 2001 Km-stand: approx. 256 000 constantly loses water, nowhere else is there to see water, so it can not lie on a leaky pipe, let’s think. The cylinder head seal was made only 3 months ago. The workshop took out the thermostat, because it has gone constantly in the red before and the fan front was permanently on, even after we turned off the car he ran still after. Jetz t is thermostat outside, today he went up on the highway again in the red. We had the engine off, there was the balance tank half full, however at the start of the car the tank was empty, you could see it correctly how he had sucked in the water. If we drive e.g. highway he pushed Wassr out, always piece by piece.. And where he went as said in the red and the red lamp already started the Volvo went down with the gas by itself, he got slower and slower, the gas pedal was like blocked.. We don’t know any more… But since Thermostat was out, the fan at the front is not asoo many times as before.. That’s why we thought it was because, but as I said today, the same theater again.. Has anyone ever had experiences with it??? What could it be??