07 Spec5 fuel mileage

Now have about 5000 miles on the "little one", and the mileage is varying widly, and I'm wondering why. It goes from the low 20's to the upper 30's
from week to week with anything in the middle of that range. I can tell when it's going to be good or bad by how many miles it goes before the gage needle drops off of E on the gage. AT about 50 miles if it drops off E, lousy mileage. At about 100 to 100+ miles the mileage is great. Thought maybe might be the pumps at the station but realized that I take the other car to the same station, use the same pumps and it's mileage it pretty consistent. What gives? Do they do this before fully broken in? Can't tell any difference in the way the engines runs thru the different fill-ups. It will go to the shop as soon as I get a chance, but for now maybe someone has seen this and can give me an idea as to what's going on with it. Thanks.
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Paul O.
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I am assuming you mean 'dropping of of F' not E. If true, it sounds like you aren't always topping off to the same level when you fill up. Many cars will let you 'stuff' in an extra gallon after the pump automatically shuts off. The pumps' shutoff point vary wildly from one to another. You need to use the same pump at the same station if you want to use the fall off point from F as a guide. Personally just recording the mileage and fuel usage should be far more accurate. As to the varying mileage, does anyone else drive the car? Their driving habits may be quite different than yours. My 19 year old son destroys! our mileage, as you can well imagine......
Tom

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Yeh, I meant F, brain not working I guess. The only other driver is the wife and it is driven about the same every week. I tried getting more in it after the pump shuts off, but the pumps go just a few tenths of a gallon and keeps clicking off. The other car(not a Kia) is filled at the same station using the different pumps with pretty consistent mileage.
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