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Old 06-23-2012, 12:52 PM   #1029
suss6052
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Join Date: Feb 2012
Fan#: 95752
Location: ..., MI
What I Drive: 2013 Ford Focus ST2 Ingot Silver

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Quote:
Originally Posted by FordFocursing View Post
I'm very excited for all these high mpgs being reported, but urge folks to hand-calculate to confirm.

I hand verify every tank (with the added advantage of almost always using the same actual pump) and found that not only is my car's computer off, but not really by a predictable margin (or even direction). I asked my dealer about this and the responses was "You're lucky it's not off by more!"

This is my first car with an on-board mpg calculator, but my reading indicates that they're more novelty than scientific reality across the board (brands, models, etc).

I, too, have gotten 40+ mpg readings on trips -- felt like a million bucks -- until I did the math myself and saw I was still in the 34-ish ballpark.

Anyhow, don't mean to be a buzzkill, just suggesting folks consider their hand-calculated mpgs along with dashreads.
I've always done the hand calculations, and that while the dash computer so far hasn't been consistently off either high or low yet it has generally been close, but I only have 5 fuel ups since new. When I got my highest average tank mpg the computer was saying that for trip 1 I had gotten 37.8 mpg average. However when I filled up the tank to one click past the auto shutoff as I had traditionally done with my last car it used 11.4 gallons to go 426 miles, which came out to right around 37.4 mpg, so it was only off by less than 0.5 mpg, but that extra bit of fuel can be enough to throw off the calculation. My average based on hand calculations over the past 1622 or so miles (up to and including the 5th fill up, but I have over 120 more miles on the current tank of gas) has been right around 34.4 mpg. However most of that has been done in town on most of my commuting tanks with only a few miles of highway per direction, and plenty of traffic lights. Occasionally then the computer will fluctuate between 29-35 mpg then. I also tend to use the a/c a lot when its warm to hot out simply because I can, and the fact that my previous car didn't have working air conditioning so I would have to either keep the windows up and really suffer, or endure the wind noise at freeway speeds.
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