600km on 90L of gas works out at 18.8 miles-per-gallon in the old money..
Fuel Consumption Calculator

Bearing in mind most 4wd vehicles are about as aerodynamic as a barn with the door open so they're never going to be thrifty to run..

My Mitsi van is only a 2L 4 cylinder petrol, but 18mpg is about the best it will do.