The bottom one is your instantaneous fuel consumption so what you see is correct. The more you press the accelerator the more fuel you use lift off and you won't much so 999.99 is you freewheeling and under acceleration you will get as low as 3-4mpg.
Please don't get stressed worrying about your mpg. The other reading is your average mpg which should be more stable unless you reset it to zero. It should read anything from 22mpg to 35 or more depending on the type of driving you do.
The fuel range does change but is also calculated using your instantaneous fuel consumption. These all settle down the further you drive.
Use the gauge to decide when to refuel don't always believe the range reading.
Please don't get stressed worrying about your mpg. The other reading is your average mpg which should be more stable unless you reset it to zero. It should read anything from 22mpg to 35 or more depending on the type of driving you do.
The fuel range does change but is also calculated using your instantaneous fuel consumption. These all settle down the further you drive.
Use the gauge to decide when to refuel don't always believe the range reading.
