Thank you for the comments.
At this time i have a Volks golf diesel 2000 and i manage to get my 6l/100 km (around 40 mpg) and on average i drove 12 000km per year but this could change.
Got another question that pop to my mind this weekend
can anyone share a graph where we could see the fuel consumption based on the load of the ICE.
Has i understand, with the volt we should talk in hours of operation instead of KM. the RPM should be in % of load instead of rev/minutes... ( if one exist)