Hi All:
___Not to bemoan the obvious but if you are calculating total FE over a tank, you really should use distance traveled over gallons purchased.
___If you are test driving an automobile of whatever sort, the FCD’s are probably good enough and better then you might have expected. You may not be generating much of an error over 1/10 of a tank vs. a whole tank and it is the comparative difference that you are interested in over that much shorter distance anyway. An Example. You refuel to top off, travel 50 miles and refuel to top off again. Are you going to show the same delta (let us assume you see a + 1.5 mpg delta over an entire tank) between the FCD and actual over 50 miles as you are over 1,000 miles or does the delta increase/build in over time/distance traveled? In the Accord, the delta builds in as your distance increases. The further you travel the higher the delta pushing to some finite difference between actual and calculated. It will not increase to infinity but approaches some built in absolute delta? In the case of the Accord, I think it is around 1.6 - 2.0 mpg. Since the NAVI was replaced in the Accord, I have consistently seen a 1.2 - 1.9 mpg overestimation by the TC vs. actual after 900 + miles. On the one short tank I have (I topped off at slightly less then ½ full the night before Katrina hit N.O. to save a few $’s), I only showed a .84 mpg delta after just 582 miles. I cannot say for sure if the delta builds in towards a specific over/under estimation with the HCH/Prius II/Escape HEV, etc. like the Accord but I bet it does? This would leave you with the FCD as a very good indicator over a much shorter distance by comparison to a whole tank.
___You can definitely use the FCD if you are calculating one segment vs. another as was the case of my first time behind the wheel of a Prius II. Here is that example:
Quote:
Initial tank odometer showed 375 miles @ 59.7 mpg --> 375 miles/59.7 mpg = 6.28 gallons
501.1 miles @ 65.5 mpg --> 501.1 miles/65.5 mpg = 7.65 gallons
7.65 gallons - 6.28 gallons = 1.37 gallons consumed
126.1 miles/1.37 gallons = 92.04 mpg
Beginning of Essex Road: 59.7 mpg
End of Essex Road: 60.5 mpg
Beginning of Essex Road: 61.0 mpg
End of Essex Road: 61.6 mpg
Beginning of Essex Road: 62.0 mpg
End of Essex Road: 62.5 mpg
Beginning of Essex Road: 62.9 mpg
End of Essex Road: 63.3 mpg
Beginning of Essex Road: 63.8 mpg
End of Essex Road: 64.2 mpg
Beginning of Essex Road: 64.6 mpg
End of Essex Road: 65.0 mpg
Beginning of Essex Road: 65.3 mpg
Carl’s exact same parking spot at work: 65.5 mpg
|
___The difference between segments will not show the FCD error at all because you are not measuring the actual, you are measuring the difference between segments via estimated gallons consumed and the FCD error should be equivalent in any given segment.
___Let me know if your hybrids FCD’s act similarly to that of the Accord as this would be an interesting piece of knowledge for future discussions …
___Good Luck
___Wayne R. Gerdes
___
Waynegerdes@earthlink.net