My 2.5 TD and questions about questions…

Hello people, after I have my AT-gear in control now to some extent, suddenly quite different questions appear: Temperature problem: in summer times fast over 100°. I found a lot about it about the SuFu and then settled with it. BUT: Yesterday I made an oil change, with filters, theFi and LuFi. I drive every day about 35 km to work, of which about 30 only BAB, and that is like: Cozy open track, 5 km max. 120, then max. 140, everything with cruise control. Ke Kühmitteltemp at about 85° according to the display. Briefly through the village, kept at the baker, again in the car, Temp is then on Min, so pointer lies horizontally…. Before the oil change up to 85-90° and then stayed so until I stood at the job in the parking lot Have also had CO-test done, because I refill water from the beginning (end of June d.J.) at the beginning, at the beginning more, now perhaps 0.5 liters on 1000 km. Result: Nothing can be faked. Then the type has the lid of the balance tank against a pressure gauge g “Ohoh, 2.5 bar, the ZKD’s gone” Can it be that way? If it doesn’t press water out of the balance tank, should I not have more loss, is it steaming, is the motor owner wet??? Does it all fit together somehow? – low temp and ZKD damage? It airs well, quite calmly, pulls well, so actually everything in the green area… Greetings from the South Palatinate, Andreas