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Discussion Starter #1
I recall having seen some FE threads where the car has recorded better FE than the owner calculates based on the volume of fuel put in at the pump. Could the difference be due to evaporation of fuel at the time of fill up rather than inaccuracy in the Insights on-board measuring system?
 

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It is believed to be excess vapors churned up during fill-up, then purged by the EVAP system. The symptom fades out within very few miles _when_ is does happen. Which is erratic at best. The lean burn window opens wide. I can climb slight hills while maintaining lean burn at an MPG that's otherwise imopssible.

The MPG indicator is "false" because of this unmetered path of excess gasoline (ever how slight) allows a more robust lean burn window.

HTH! :)
 

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I don't think that's quite what he was referring to: that sort of behaviour is observable in other cars with a fuel efficiency display, not just the Insight.
 

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Foxpaw said:
I don't think that's quite what he was referring to: that sort of behaviour is observable in other cars with a fuel efficiency display, not just the Insight.
Yup! :)

Not that you mention it, I can read it the other way too. :)

The answer there would be no. Its a closed system with very little lost due to evaporation.

HTH! :)
 

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Discussion Starter #5
Interesting responses - thanks. What I meant to refer to was evaporation of fuel at the fuel tank filling point while it's streaming into your tank. I remember reading somewhere that the amount of fuel that gets metered by the bowser (what your pay for) is not what goes into your tank because of evaporation while you're filling up. What I was wondering was whether that might explain the difference (or at least some of the difference) between the FE measured by the car and the FE calculated by using the miles travelled and the fuel consumed according to the bowser.

I know that once the fuel is inside the tank and the cap fitted on the car's fuel system is a closed loop and I imagine that losses to evaporation are very small (if anything at all).

I know this isn't a very important question - I was just wondering that's all.

Thinking about it a bit more - the amount of fuel lost through evaporation is probably so small as to make no measurable difference to recorded FE. I think I may have answered my own question.
 
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