I have this scenario, it happens a lot actualy! I like using Shell fuel as it tends to get better mileage and is cheaper too. My nearest Shell is 25 miles away, but foolishly i've let my tank run low, and now i'm not sure if I can make it.
So if I were to add say 2 litres at my local, and keep the trip odometer running until I got to Shell garage, and then filled it right up, when I came to adding it on fuelly, would I simply add the extra miles and add the two litres on at the end? If I added the 2 litres as a partial, it would not calculate the rest of the 700+ miles on the tank ive just used would it not?
I've done what you've described on a couple of occasions.
Generally if I'm in a rush to get somewhere and NEED gas. I'll throw in a buck or two of fuel, and then fill up after I've run the errand I was late for. I can then add that $1-2 worth of fuel to whatever my actual fill-up is.
Another scenario I've done with the wife's car is it's Wednesday, and payday isn't until Friday.
Makes sense I guess. I suppose it's similar although not as extreme, as when some adds together 2 or 3 fuel ups and enters them as 1 entire fuel up, which can be a tad misleading as it throws the stats such as "best miles per tank" and the like.
Anyway, I didnt end up going the way of the Shell garage, so bit the bullet and fuelled up locally
Your fuel log has no way of knowing the difference between getting all your fuel at one place or adding a little bit to get there, as long as you calculate in the total fuel added and distance. Your plan is fine. I do it all the time.
I do it, but more extreme.
A local grocery store awards points for discounted gas. When they are due to expire, I fill up the wife's car and nearly 15 gallons worth of gas cans. I'll top off from those cans until the next time to use the points.
I should just file a partial fill, but I am in the habit from the old Gassavers system which didn't have a partial fill option. If you do this while a large volume of fuel, like say a 5 gal can's worth, or even regularly with smaller amounts, it will throw off some of the statistics Fuelly generates, like miles per tank.
Like you say, I think you'd get real tired of emptying the tank again, plus you'd loose some via fumes/evaporation, not to mention spillage (it's impossible not to spill fuel!) so it would probably work out worse!