In short, the distance to empty function on your trip computer will not remain accurate with your new tank. Your vehicles ECU has the volume of the original tank calibrated to it. As the Distance to Empty counts down, the float starts to move from Full to empty, because the volume of the tank has changed dramatically without changing any reference data for the ECU to base it’s calculations on, the Distance to Empty is incorrect.
Your fuel gauge will remain accurate, as the float inside the tank will indicate how much fuel is inside the tank, so your readings going from Full, to ¾ to ½ right down to empty will remain accurate as it is now. Your average fuel consumption calculations will remain accurate too, just not DTE.
What we tell our customers is that most or our Long Range Tanks will tend to ‘hang’ on full for a while longer than it did originally, simply put there’s more volume to be used before the float starts to move downward. Your low fuel warning light will work as intended.
The best tip we can give you is to reset your trip meter every time you fill your tank, over time you’ll be able to establish how far you can travel in different driving conditions.