Partial Fill Screws Up MPG Calc...

[ember1205]

...once you get back to a filled tank.

Why does Fuelly add in the previous gallons of fuel but doesn't bother to add in the previous miles? This is flat-out stupid!

Partial Fill done on 6/26/20 with 312 miles driven and 7.695 gallons of gas.
Full Fill done on 6/29/20 with 181 miles driven and 13.837 gallons of gas.

Fuelly added the fuel together to get 21.532 and then calculated that amount of fuel used over ONLY the 181 miles for the full fill, resulting in 8.41MPG (and nothing entered for the previous fill).

I am completely confused at how the "math" for this site works and have always complained that two consecutive full fills were NOT necessary to calculate MPG so long as at least one full fill had been recorded somewhere in the past. Now I understand why two consecutive ones are required - it's because Fuelly isn't smart enough to track both miles AND fuel quantity as cumulative.

SMH

[Draigflag]

I don't think you entered it properly, I saw the fuel up in question and the amount of fuel you put in on that fuel up is too high. Its even higher than some of your previous tank. A partial fuel up is when you don't fill the tank right to the top, example, you only put a gallon or two in because you want to use a cheaper filling station further down the road.

[ember1205]

Originally Posted by Draigflag

I don't think you entered it properly, I saw the fuel up in question and the amount of fuel you put in on that fuel up is too high. Its even higher than some of your previous tank. A partial fuel up is when you don't fill the tank right to the top, example, you only put a gallon or two in because you want to use a cheaper filling station further down the road.

I'm not sure how you reached that conclusion...

Full tank
Drive 312 miles (tank is close to empty), but only add 8 gallons, tank about half full.
Drive 181 miles, fill tank (close to 14 gallons).

The tank starts full. I drive a full tank's worth but only bring it back to half. This fill-up is marked partial and it calculates no MPG. Drive until tank is close to empty and completely fill.

Fuelly calculates the MPG using ALL of the gas added but only the most recent miles. If you add the fuel and miles together from the partial and the complete fill and average them, you get almost 23MPG which is roughly what would be expected.

[Draigflag]

The 312 mile tank is the partial one, the one after, 181 miles, is a regular fuel up, you can't have gotten that much fuel in after a short distance. With method of tracking are you using?

[ember1205]

Originally Posted by Draigflag

The 312 mile tank is the partial one, the one after, 181 miles, is a regular fuel up, you can't have gotten that much fuel in after a short distance. With method of tracking are you using?

The tank before wasn't full. So, yes, I absolutely could put that much fuel into the tank for the complete fill. Re-read my follow up post to understand the process...

I had a full tank and drove until almost empty. Partial fill. Drove until almost empty (which is going to be a much shorter distance since I wasn't starting with a full tank). Filled the tank.

I track by odometer.

[trollbait]

Previous partial fills were calculated correctly.
This is probably a bug that came up with a recent update.

[ember1205]

Originally Posted by trollbait

Previous partial fills were calculated correctly.
This is probably a bug that came up with a recent update.

Yes, I did notice that a previous partial and complete fill combo did seem to calculate correctly. Are the calculated values stored and retrieved when viewing a page? Why aren't they calculated each time? I would think that partial/full fill combos would be either all correct or all incorrect.

[EddWick]

Hmm, I wonder if OP was already able to solve this.

[ember1205]

Originally Posted by EddWick

Hmm, I wonder if OP was already able to solve this.

It really isn't my problem to fix...

[ember1205]

Just to add a little more info to this...

I have recently discovered that entering the data via the mobile app (which appears to be nothing more than a slimmed down version of the web site) causes an MPG calc issue once you finally fill the tank. And, all you have to do is edit the fill-up from a web browser and save it and the MPG calc gets corrected.

Data:

Fill tank
Drive 300 miles
Partial Fill 0 no MPG calc
Drive 150 miles
Fill tank - MPG uses total miles driven divided by only current gallons (this time, it calculated 7MPG).

View history for the car using a computer / web browser and there's an icon stating that the current MPG info include the prior partial fill data.
Click the pencil icon to edit the full fill-up.
Click Save.
MPG now shows 22MPG.

Something is wrong with the way the system is calculating MPG. It -appears- that it's calculating MPG at the time that the record is saved and storing the number instead of actively calculating when the history is displayed. Editing and saving the record using a web browser is clearly doing something differently than when the info is initially calculated using the app...