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I've mentioned before my glee at the excellent gas mileage from my 2017 Smart Prime cab. Substantially better than my 2013 was! I just drove the 1 1/2 hours from Bloomington IN to Indy averaging 54 mpg.

But the mileage varies in unexpected ways. I sometimes drive about 25 miles on a particular drive through isolated state highways with mild hills, 40 - 45 miles her hour on the average. I average 48-50 mpg.

I did so one weekend, then on the following weekend, in identical weather, identical wind conditions and the same tank of gas, I averaged 37 mpg. Even the same time of day. I can't isolate a single defining difference that might easily account for this difference. During the following week, on a new tank, mileage remained low.

Any helpful thoughts?
 

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Exactly why gas mileage should be averaged over multiple tanks of gas. some pumps deliver fuel at a faster rate and cause the gas to foam and fool the shut-off into thinking it is full when it isn't. thereby looking like you got more miles on less gas, the next tankful takes more fuel and makes it look like you used more gas on less miles.

Even using the same pump, at the same time of day, same temp, and same route can be affected by humidity, barometric pressure, wind speed, temp of the tires, pressure on the gas pedal, weight in the car, etc. There are also variables inside the motor and transmission that can affect MPG as well. Averaging over at least 3 (or more)tank fulls will give you a better indication.
 

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If the OP can not replicate the earlier 48-50 mpg with future tanks of fuel then there may be reason to investigate further. If they are on the same tank I suspect they are referencing the display for fuel consumption and not actual physical consumption.

Track many tanks and see how accurate the meter in the car really is, you may find you do not want to trust it at all. There are known issues with the fuel gauge in the 453, it would not take much error to throw off the consumption meter in the car.
 

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Discussion Starter #4
Exactly why gas mileage should be averaged over multiple tanks of gas. some pumps deliver fuel at a faster rate and cause the gas to foam and fool the shut-off into thinking it is full when it isn't. thereby looking like you got more miles on less gas, the next tankful takes more fuel and makes it look like you used more gas on less miles.

Even using the same pump, at the same time of day, same temp, and same route can be affected by humidity, barometric pressure, wind speed, temp of the tires, pressure on the gas pedal, weight in the car, etc. There are also variables inside the motor and transmission that can affect MPG as well. Averaging over at least 3 (or more)tank fulls will give you a better indication.
Huronlad is correct. I used the dash computer and monitored the mileage for each trip separately. As mentioned, the temp, humidity, wind speed, pressure on the gas pedal, path traveled, weight in the car, etc, were as close to identical as I can imagine. And same tank of gas. But under any circumstances, it's difficult to account for the substantial 13 mpg difference.

Of course everything you say, jimvw, is correct, and I very much appreciate your comments! It seemed like the lower gas mileage continued for a tank and a half, more or less, then returned to high mileage, but outside of the aforementioned identical trips example, I cannot be certain how much these factors differed and effected things.

I've tracked 32 tanks of gas since I purchased the car using the iPhone app "Gas Cubby,", and with each fill I reset the dash computer mileage gauge and compared gas usage with that dash computer results. They seem quite similar, leading me to believe the car is correctly tracking mileage and gas usage.

What surprises me is that no other forum members seem to have indicated these types of inconsistencies.

Under any circumstances, I'm generally thrilled with the mileage I get on this car! (54 mpg traveling to the Smart Dealer in Indy from Bloomington the other day!) I'll continue watching. Unless there's serious reason for concern, I can live with occasional inconsistencies. Thanks to both who have replied!
 

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I did monitor my first car religiously for 167,000 miles and the wife always seemed to get in the 53 range on drives up to the cabin, while I could get 50 ish occasionally, but mostly in the upper 40 range. Still better than the 15-17 MPG in my Expedition so I can't complain.

Truth is I got this car for it's low purchase price and the fact that it is fun to drive. The MPG is just an added bonus!
 

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Tank by tank differences..................

Every thursday I attend a meeting that ends at the same time. On the way back home,I stop at the same gas station to top-off the tank. I always use the same pump/nozzle,and use the same method for filling. Insert nozzle fully,pump at steady rate
until pump shuts off. Withdarw nozzle 2inches,wait for foaming/sloshing to settle,pump again until pump shuts off again. On
my 2 most recent fill-ups I got 3.2 gal for 144miles=45.0 mpg. On the next tank 3.6 gal for 140=38.8 mpg. So 4 fewer miles
traveled,and .4 gal more used,lowered MPG by almost 6MPG! I live in the mountains of NC,and drive hard (speed limit+5mph)
in town,2-lane,or 4-lane. I avarage best MPG on long trips,and summer driving,and flat terrain..............
If you are interested in an accurate MPG number for your car,you need to average it over SEVERAL fill-ups! The best free
website to do this is Fuelly.com. You sign in, enter miles and gal.used,and they keep a running average MPG for your car! You
can also view average MPG for every make,model,and year car.......................
 

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well over 3\4 of my miles are to work and back. same route, same station for filling up, same method. variables are weather and temperatures, and traffic. Most of the time, there isn't any traffic as I work 2nd shift. I do see a fluctuation in mpg occasionally but I just don't worry about it.
 
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