Consumption 451 CDI 54PS

Hello everyone here, the diesel consumption of my 54hp CDI fluctuates very strongly. There is everything from 3.3 l to 6.5 l. Only ARAL is refueled at always the same gas station. When I picked him up last November and drove 200 km home (110 km/h-120 km/h) he used 6.5 l to 100 km. At that time he was not in good condition. I think he had stood long or much short distance with it. The diesel was very loud and he was rather lame. Meanwhile, 8tkm later, much has been renewed and it runs very well, overtaking trucks on the highway also goes uphill without any problems. On my way of work. 25km easy distance 90% motorway and around 90 km/h speed he consumes in winter, -5°C to 0°C 5.5 liters and it takes 15 km until it is halfway warm in the car. In summer it is more 3.5 to 4 liters to 100 km and the heating is right after 5 km on the bollard. Is that so normal or there is something I could check out for 2011 The Pure P.P.