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Query on erratic gas usage.

898 Views 6 Replies 4 Participants Last post by  jimvw57
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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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 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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