Can anyone explain why my MPG on the NAVI INFO screen always shows more than the actual MPG? I always reset everything, but there is a huge difference.

The NAVI shows 26-ish, but I'm only getting 23-ish!

The actual mileage on the odometer match the NAVI INFO screen exactly.

 

Because that is basically just a guesstimate. The computer can only account for so many things and display what it comes up with. I wouldn't expect mine to be accurate. +/- 3ish mpg seems reasonable.

 

^^ that.

 

Concur with what is said. How are you calculating your mpg?

I reset my odometer every fill up and when I fill up again I just calculate miles driven that session by how many gallons it took to fill the tank completely.

I get +/- .5mpg difference generally.

If were talking about miles left till empty feature, its off by 2 gallons or about 40 miles.

 

My MPG as indicated by the Navigation has almost always been spot on to what it is when I divide my miles traveled on a tank by how many gallons it takes to fill it back up. I don't check the two methods of fuel economy measurement against one another that often anymore, but it always used to be relatively accurate when my car was newer to me and I cared and was curious enough to regularly compare the two.

Don't forget that not all gas pumps aren't 100% accurate or perfectly calibrated to match up with every other pump at the station. There are people from the Department of Weights and Measures who have the job of going around to gas stations every year and making sure their pumps are within a tolerable range of accuracy, or the station can be subject to a monetary fine... but there's no guarantee that if you pump in 18 gallons of gas according to the pump, that you aren't actually putting in 17.2 or 18.5 gallons of actual gas if it were measured 100% accurate.

Even if the pump that you use to fill up is 99% accurate... if the pump tells you that you put in 20 gallons of gas at the station, you could still be off by 1/4 of a gallon over the course of that supposed 20 gallon fill up. Your calculations of MPG as computed by taking Miles traveled per tank divided by gallons put in to fill it up will only be as accurate as the accuracy of the calibration of the pump that you use to fill it with.

 

I divide the number of miles driven by the number of gallons it takes to the top. Each time it is off by around 3 MPG compared to the NAVI calculation.