XC60 BJ 2011 – Coolant disappears/cooks + pressure on hose!!

Hello dear community, I bought the following Volvo: XC60 I 2.0 – D3/D4 – 163PS – Diesel First registration 2011 Unfortunately I bought the car from a fraudster (KM stand was turned down from over 300tsd to 110tsd). The car is still running great, but I have the following problem (date at Volvo partner workshop only from 26 July possible!!!): When driving lights up from time to time that cooling water is low and the car should be parked immediately. However, the Then suddenly again. If you stop, a lot of pressure has always been on the hose. The level of the water was then always below minimum. When carefully opening the lid of the cooling water, then always air came out, so air pulls and has a pressure. Then the stand goes up again to almost maximum. Meanwhile, however, the water also cooks extremely, which is why we worry. This time he also loses cooling water, so that we always refill. Has someone with it already He What could it be about? Should you wait for Volvo? Is it worth a repair, since the car actually only has a value of 2-3 thousand euro(?)? Maybe I can find someone who has a little more information about my problem. Thank you!