Fuel consumption too high ?!!! Pt. Cruiser

Hello dear cruiser community I have the following problem and hope that you can help me, and that my little one somehow consumes too much. If I can get 7 liters of tank I only get about 51 KM far instead of 70! Lt. guide should the cruiser drive 80 km with the reserve tank?! Does he at least certainly not! With full tank I come about 420 km… That’s not normal?! Have you ever had experiences with it, you know why the high consumption l Ps.: Have the cruiser as automatic, gasoline dear greetings and many thanks!!!