Still don't understand "partial fuel-ups"
 

Still don't understand the "partial fuel-ups" concept. I read the FAQ (article: "How do I account for partial fuel-ups?")

So can someone answer this please? Is everything considered a partial fuel up, unless your car runs out of gas completely? or am I interpreting it wrong? I usually fill up when my car gets down to about 1/4 tank or less. Are these considered partial fuel-ups? I can be dense, but I think the FAQ article may need to be re-written so fools like me can be clear on this concept ;)

Advice is appreciated.

No, you're interpreting wrong. A partial fuel-up is when you can't fill the tank all the way to the top.

If you fill up your tank, drive for ten miles, stop for gas, and fill up to the top again—that's a full fuel-up.

If you go to fill up, add $5 worth of gas without filling to the top—that's a partial fuel-up.

Because Fuelly uses the difference from full to calculate individual fuel-up MPG, it needs a full tank to work with. If you don't have a full tank, the individual MPG calculation for that fuel-up and the next one is going to be way off. So you can let Fuelly know you didn't fill to the top and it will pick up again once it has a full tank to work from. Here's more info: Why do I have to fill the tank all the way up every time I buy fuel?

I guess you can also think of the word partial as meaning not full to the top.

I have noticed a flaw with this theory. In the UK, most people can't afford to fill their tank! I guess the average car here costs the equivalent of around $130 USD to fill. Luckily, my tank is small (35 - 40 litres) but most people i know only buy between 2 or 3 gallons due to the high price ($8 to $10 a gallon)

Fill it to the brim each payday & put those tanks in as full tanks (that way fuelly has something to work on). If you fill up more than once between each payday you're not saving yourself anything by shortfilling.

That's not really a flaw with the theory. MPG (L/km or whatever you use) is determined by using known quantities, distance and volume (miles and gallons for me). Without filling the tank between two fill ups, it's impossible to know how many gallons have been used in between. Putting in 2 gallons today and adding 4 next week doesn't mean you used 4 gallons. Filling your tank today (regardless of volume) and driving then adding X gallons to reach full again does mean you've used X gallons.

The theory still applies, whether you can afford to fill up or not. As Draigflag mentioned, you're not saving anything by NOT filling up. You'll use the fuel either way.

@Draigflag Really? Most people you know can only afford to put 3 gallons in thier tank? Why do they have a car then? I find that just a bit hard to believe. Now I know some people only want to put fixed amounts in(such as 50 euros) to help keep track of how much they spend on fuel. But that isn't the point of this website. It's point is to give honest fuel consumtion figures.

The only way you could use a partial tank theory to accurately calculate mileage, is if you started with a bone dry tank, put in 4 gallons, drove it till it was bone dry again, then you could calculate mileage for those 4 gallons, using odometer readings from the empty to empty cycle. Problem with that is, you have to run out of gas all the time to be accurate.

So the best way is to use full to full tanks. For those with hard money issues, don't let the tank get less than say half full. Keep it full, rather than run around on empty. Its easier to put 2-3 gallons in it to keep it full and easier on your pocket book, plus that way in the case of an emergency, you HAVE plenty of gas when you need it. :D

Plus you can accurately track your Mileage that way.