From what I've been able to determine, the issue here isn't that the gas is disappearing "all of a sudden"; it's that the fuel level gauge doesn't update while you're driving. It *only* updates when you get out of the vehicle, where you'll see the gauge suddenly drop.
That said, fuel consumption is currently *through the roof*; just driving from my base to the nearest gas station (a relatively short trip) consumes 25% of the tank. Carrying a jerrycan in the car is an absolute necessity at this point.
