Cooling water is pressed from the cooler into the balance tank!

Hello everyone! It’s about a Mitsubishi Galant 2000 TD GLS (66KW-90PS) Built 1999 – 140000 km The cooling water is pushed out of the cooling system while driving into the balancing tank, there is also a lot of pressure on the hoses. Effectively the system loses water. After 700 km of highway more than 1 liter of water had to be detected again. First guess was the cooler cover (was also changed). Next the cylinder head was removed, on cracked checked (head was tight). – no cracks, it was only planned about 0.20 mm). New ZKD was installed, new thermostat and new timing belts, with new ZK screws. After that the water level was fine, but still pressure was on the hoses. After 7 days he pushes the water back into the balance tank. Maybe someone successfully solved the similar problem with the model. PS: No oil in the water and vice versa! no white smoke when exhausting! engine does not overheat! both fans switch on n! Thank you very much for your help!!!