Thought I would share with the Rover World. Drove about 4 hours yesterday all on freeways in SoCal and retuned almost 21 MPG? Is that even possible on a Rover V8?!

 

Check the math on that computer by restarting the trip odometer when you fill up the tank. When you refuel, fill it back to the top - you now have gallons and miles to get an actual mpg calculation.

 

Right, Not possible. The OBDII port has no way to measure actual MPG, It is not a function of the ECU, it is just an estimate based on user input.

As mentioned the only way to really know is the old fashioned way... And use a GPS for you actual miles rather than your odometer... Could be off by as much as 5%.