Snowcat said:
I filled up a day ago, and initially the range went to 596 miles, then 609, then down to 546. Having done some 60 miles since then the range is now showing about 420. On a separate occasion I did an 80 mile round trip, and when I got home my range had increased by 40 miles. Some fuel monitor! Does anyone else notice that the range is very erratic and recently so misleading I nearly ran out of fuel.
The distance to go calculation needs to know two things - how much fuel is in the tank and your average fuel consumption.
The information for fuel level is the same as the traditional fuel gauge - a float moving a potentiometer. It is inherently crude. Also, the float hits the top of the tank before the tank is full, so some miles need to be covered after a fill before the float can start falling.
The fuel consumption is reasonably accurate because fuel delivery is controlled by the ECU which sources the information for the dashboard. But for DTG purposes it depends on when a reset last took place. The average fuel consumption will fluctuate a lot after a reset but smooth out as distance builds. I don't know about the 208 but if you have not reset manually, some systems auto-reset when they see a large increase in tank level.
Thus, both engineering and maths contribute to the limitations so best don't expect a reasonable indication until about half the tank has gone. It is then likely to be calibrated on the pessimistic side (ie, to get you fill up sooner rather than later) as the tank nears empty. (Did you really "nearly run out" or did the last 80 miles or so just drop very rapidly?)