I know why now,
IMO the l/100km caculation is based on E/T, the distance travelled and the fuel used .
I did a lot of pre heat and post heat when I bought the car, which means she uses the fuel, E/T is increasing but the distance stays.
Those made l/100km higher and gave weird distance readings.
So, I reset the travelled distance and avoid pre/post heat and now everything works fine.
