I half *** searched so let me apologize now. I am curious to know why when I gas up the car (i completely top it off) I can get the "avg" mpg display to almost 75 mpgs (going 55 mph on a 20 mile commute) but on my way home it goes down to the low 50's and my speed is still the same.

It appears the less fuel in the tank yields a lower "avg" mpg read out. Have any of you noticed this?

One more question for the hyper milers...for weight savings, are you filling it half full, drive to empty then refill half way, to keep weight savings down?

because on the way to work you are losing altitude and/or the wind is in the same direction as your heading. On the way back you are probably gaining altitude. I experience the same thing but not as much. On the way to work I can get ~50 mpg, on the way back it drops to 46/47.

Where are you located? Any idea what the altitude of your house and office are? That sounds a little like the drive from my house to the airport. It's only 10 miles, and only slightly down hill, but I've been over 120mpg getting there (usually about 90mpg though) and can only manage in the high 50s home--even with a warm engine.

I'm sure that the weight of gas plays some roll, but in my day to day driving I don't notice much of a difference between a full tank and an empty one so I doubt that's the reason for your difference. Besides, over the course of your 40 mile round trip, you are only burning .63 gallons which probably weighs about as much as the Chipotle burrito you had for lunch .

Commuter car, grocery getter, and summer road tripper--average 10k miles per year.


Winter road trips and ski trips, bad weather commuter and my wife's "daily" driver--expected average 4k miles per year.

I live in Gilbert AZ and work in Phoenix. The thing is, I can't replicate the the 70+ mpg's again till I fill it all the way back up.

Do you only reset when filling up? Could it be because of the averaging of the return trips?