Our Jeep is the same way. The average reading will say 13-14 and miles traveled divided by gallons is more like 11-12. Sometimes it's better than others. I started reading up on why and found out that the average is only the average over the last 50 miles! So if I drive it for the first 200 miles then my wife, the last 50, it's about on, since the readout is still optimistic. The other way around, it's just WAY optimistic.
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