Just got a 2014 3i. I've always been an MPG tracker. I reset the avg MPG each time I get gas, usually about 10 gallons at a time. The avg mpg display is anywhere from 1 to 1.5 mpg higher than manual calculation. Why?

 

Like all vehicle's with the AVG MPG tracker, it has a +/- of a certain percent. I have heard of many Mazda's that are dead on when it comes to the MPG reading, so the owners say. There is nothing that can be recalibrated or repaired to my limited knowledge.

 

It depends on a ton of different factors, especially how accurate your odometer is. Pretty much every car is going to be at least a few percent off when measuring speed/mileage.