Quote:
Originally Posted by neilzero
I think the problems with frequent small fill ups is exaggerated. If you average over 50 gallons it should not matter if this was 4 fill-ups or 10 fill-ups. Neil
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It's not averaged, frequent small fill-ups that is a problem, it's the individual small fill-ups.
You aren't going to get to exactly the same level every time you fill, it just isn't going to happen. The volume of the fuel in your tank is going to vary a little with temperature, the pump doesn't shut off at the same point every time (espeically with different brands), a slight incline one way or the other will affect the fuel level at the fill hose, etc. Factor in all of these and the amount of fuel in your tank will vary.
You know how much you pumped in, but that isn't how much you used since you last filled. How much you used is going to vary based on the conditions when you last filled AND the conditions from your current fill, which doubles your error. In other words, you may have been at one extreme last time and the other extreme this time.
With a big fill, you may not notice this, with a small fill it will definately affect your mpg calculation for that tank. Not a big deal if you average 10 small fills, but if you use that one small fill to determine how effective your recent mod is, then it has to be a BIG change or it will get lost in the measurement error.