Point at a vehicle and put this into one of the the debug console value check fields:
getNumber (configfile >> "CfgVehicles" >> typeof cursorTarget >> "fuelConsumptionRate")

2 more examples:
The CH-49 Mohawk e.g. has a rate of 0.138
A M2A1 Slammer has a rate of 0.01

For me these are abstract numbers, no idea how they are applied in the game. Fact is, you can drive around in an M2A1 for hours on end w/o a noticeable fuel consumption. That really limits realism in any mission.