Inconsistent Trip Computer

[groundhogday1976]

Okay, so I know that the trip computer mpg reading isn't going to be the real, calculated fuel mileage. However, I just did my third fill up in the car, and it's been very close on the first fill (actually slightly lower than calculated, 32.0 vs 32.3), about 4 mpg optimistic on the second fill (32.2 vs 28ish), and on the fill up I just did it was reading a whopping 7.3 mpg higher than calculated (33.3 vs 26.0). What variables are involved when the car calculates mpg? And I must say I was pretty shocked at getting only 26 mpg on the last tank. I'm generally pretty gentle with acceleration and run 80% highway at 75 mph with the cruise control on. I don't understand the huge difference between my first third tanks under similar driving conditions.

[seldomseen]

What's the latest on this situation?

[telcoman]

Temperature, Humidity, elevation, wind speed and direction, tire pressure are all factors that contribute to MPG.
If you want accurate MPG set the trip odometer to zero when filling up.
On your next fill-up divide the total miles traveled by the number of gallons it took to fill the tank.

Telcoman

[Rogue One]

This topic has been discussed ad nauseam in the Rogue forum chatroom-mpg-1st-2nd-gen-t601214.html

[groundhogday1976]

I've calculated mileage on every single tank. Since the original post I've gotten anywhere from 31 to 34 mpg calculated. I'm happy with that. It's still mostly highway miles, but some tanks have had more in town, at drive through, etc time and some very little. In hilly terrain, often on windy days, and going anywhere from 75-80 on the interstate I think that's pretty good for a midsize car. I think if I drove through an entire tank on the highway at the speed limit on flat terrain it might actually get the EPA rating or better. The computer has been off anywhere from under one to just over 3 mpg. Not as far off as the 7+ mpg discrepancy I reported above. I do think that my manual calculations aren't always completely accurate either. Pumps vary, and I believe that how level (or not) the slab I'm parked on when filling is can cause some variation in how much fuel the tank will hold. I think in reality all the trip computer is useful for is to show you how efficiently you're driving, to know if you're consuming more or less fuel driving in a certain manner.

[txchamps]

I kept a spreadsheet of my Versa Note S real world mileage vs. the trip computer, and decided that the trip computer offers little predictive value. topic593412.html

The results were just too random. I have noticed that on my 2015 Versa sedan, the results have been a little more consistent -- but still by no means useful. Nice gadget, but it doesn't add value if it's not consistent and accurate.

But I have never experienced the calculated mileage being higher than the trip computer's measurement.