When using partial fill ups... - Fuelly Forums

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Old 05-17-2016, 09:19 PM   #1
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When using partial fill ups...

So I haven't logged anything for about a year and checking back in to fill all the info in. I noticed that I can't get the right MPG after doing a partial fill up. This reports a fictitiously high number, because I believe it's taking the miles from the partial fill up and adding them to my next entry which should be not included. I'm getting higher than average MPG which throws my All time high MPG off as well.

Not sure on how to explain but it seems like it's taking partial fill ups and then adding them to the next entry.
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Old 05-17-2016, 10:18 PM   #2
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I don't know how you can get a true mpg figure from a partial fill up at all - the only way I understand an mpg figure is to do a brim to brim fill, otherwise it can only be a guess...?!
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Old 05-17-2016, 11:58 PM   #3
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As far as I'm aware, fuelly will not calculate your MPG on a partial fill, or the following fuel up. Perhaps you missed the partial fill box on one of your fuel ups, which would throw the others off?
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Old 05-18-2016, 12:03 AM   #4
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I've looked at your fuel ups for the Audi. Fuel up number 122, you have 733 miles on one tank, your average is only 327 per tank. Is this a mistake, as it could be the one throwing out your data.
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Old 05-18-2016, 06:08 AM   #5
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Fuelly won't calculate a partial, bit I think it does do the next full fill now, adding the partial data to it. Either way, partial tank data is added to the lifetime numbers.
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Old 05-18-2016, 11:11 AM   #6
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Quote:
Originally Posted by Draigflag View Post
I've looked at your fuel ups for the Audi. Fuel up number 122, you have 733 miles on one tank, your average is only 327 per tank. Is this a mistake, as it could be the one throwing out your data.
Right. I've narrowed it down to that, and the reason why is because I have no data for the fillup, other than the miles I went between that. So lets lay out the example like this.

Fill up 1:
Have gallons, price and miles traveled. Went from 10,000 to 10,300 for example sake

Fill up 2: (friend borrows car and doesn't log data when fills)
Have miles traveled. Say went from 10,300 to 10,650

Fill up 3:
Have gallons, price and miles traveled. Went from 10,650 to 11,000.

So because I didn't have any data for 2, I just marked fill up 2 and 3 as partial. In this example I would have 700 miles per x gallons of fuel in fillup 3. In reality, that's not true mileage and I don't want to start counting MPG again until a full to full fuel fill cycle, with pertinent data. Does that make sense?

Should I just have one entry for the miles driven where I don't have any fuel data, and just leave it blank? Will that clear out erroneous data?
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Old 05-18-2016, 01:40 PM   #7
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If that is the case, just don't enter fill up number 2, assuming you are tracking distance by trip odometer.

Within the system, a partial fuel up is a fill that didn't fill the tank completely, but you still have the amount of fuel. Dividing the distance driven for a filled tank by that lower amount fuel for the partial fill would result in an incorrect figure. So Fuelly doesn't calculate a fuel economy for it. On the next full fill, Fuelly takes the data, distance and fuel, of the preceding partial fill(s), and adds it to the current fill data.

For your example that means Fuelly is dividing the distance for 2 fills by the fuel of one, and thus the error.

I'm don't use odometer tracking for distance, so I can't say how to go about entering fill in which the fuel amount isn't known.
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Old 05-18-2016, 02:13 PM   #8
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I'm just going to admit here and now, my maths isn't good enough to help sorry! I'm assuming you're using odometer tracking? This is why I use trip meter data, as it doesn't matter if you miss one or two, or 50 fuel ups, you can just track and add as you please. I believe there is a "missed fuel up" box when using odometer tracking too? Did you check this after the fuel up when your friend borrowed the car?
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Old 05-18-2016, 08:37 PM   #9
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Originally Posted by trollbait View Post
If that is the case, just don't enter fill up number 2, assuming you are tracking distance by trip odometer.

Within the system, a partial fuel up is a fill that didn't fill the tank completely, but you still have the amount of fuel. Dividing the distance driven for a filled tank by that lower amount fuel for the partial fill would result in an incorrect figure. So Fuelly doesn't calculate a fuel economy for it. On the next full fill, Fuelly takes the data, distance and fuel, of the preceding partial fill(s), and adds it to the current fill data.

For your example that means Fuelly is dividing the distance for 2 fills by the fuel of one, and thus the error.

I'm don't use odometer tracking for distance, so I can't say how to go about entering fill in which the fuel amount isn't known.
I do both, I log both the odometer and trip distance. But in Fuelly I put in miles since last fillup, so trip distance. I guess I can omit that entry. I'll play around with both tomorrow, and I guess you guys are both right, since I'm not putting in odometer readings, I can just wipe this completely off and fuelly won't know if it existed.

Quote:
Originally Posted by Draigflag View Post
I'm just going to admit here and now, my maths isn't good enough to help sorry! I'm assuming you're using odometer tracking? This is why I use trip meter data, as it doesn't matter if you miss one or two, or 50 fuel ups, you can just track and add as you please. I believe there is a "missed fuel up" box when using odometer tracking too? Did you check this after the fuel up when your friend borrowed the car?
My math should be good, I'm an engineer for heaven's sake. But I've done this before and fuelly has corrected it for me. Maybe then I was doing odometer readings rather than trip miles. At the end of the day, an odometer reading from 10,000 to 10,500 and a trip reading of 500 miles is the same dang thing.
I'll look for that missed fuel up, as I just want to be anal retentive on making sure miles are truly displayed. I've logged almost every tank of gas through both cars for more than 3 years. I'm a little data driven...
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Old 05-19-2016, 12:07 AM   #10
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I understand, I am a tad OCD about my fuel ups too, might have a meltdown if I miss one! One of the admins might be able to help, hopefully they'll see your post soon.
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