Enter in Partial Fill-Ups
 

Complete Fill-Up every time? Fuelly is caculating my MPG wrong due to my partial fill-up.

I put some gas into my car last night, only about 2 gallons, but Fuelly went ahead and assumed that I went my 355 miles on 2 gallons. So my question is am I allowed to enter partial fill ups? Maybe we need a check box allowing such? Or did I hit a bug?

Date: 8/19/08

Miles driven since last fill up: 355.0

Gallons bought: 2.040

Price per gal: $4.09

Estimated MPG: 174.0

Yeah...I wish I got 174 MPG

We're adding a partial fill-up option today. We're planning to have it added to the site before the end of the day.

Thank you! Ill just delete that entry and redo it when you add the feature.

Partial fuel-ups are available now.

I don't understand why a partial fill up can't calculate the MPG if you're putting in an odometer reading every time.

If I put 2 gallons in for a partial fill up and I went 70 miles I got 35mpg.

ozreiusn, I explain the way fuel ups work in calculating mileage on another thread.

If you don't fill up a tank all the way, it simply doesn't work even if you are using odometer. The problem is you can drive 300 miles and only get 2 gallons. Your next fuel up might be 10 gallons after only 40 miles (to make up for the low fuel), but the non-fillup and followup throw your average completely off.

Here is a spreadsheet with test data, assuming I have a 20 gallon tank and my car always gets 20 mpg (and the odometer started at zero with the first fill-up).

You can see from the data that the non-fillup throws the MPG way off into the 150mpg range, and the subsequent 2.67mpg fill up doesn't bring the average back to 20mpg