Could the site add a provision for fuel additives? I see improvements in mileage every time I add a 12oz bottle of fuel system cleaner. I know it is only .107gl but it has a cost and it affects mileage.
This is what the notes feature is for. You can click "Add a note" on the left and put in your odometer reading at the time you added it, and any details about the additive. If you add it during a fuel-up, you could note it there in the notes too.
Notes are set up to handle any extra info that could affect your fuel economy.
I think (and I could be mistaken) but it seems they would like to be able to add in the cost and effect of using the additive as part of the fuelly features. Naturally it isn't documented anywhere, as it is not a feature.
The "add a note" feature is there to simple do that. Add notes about anything relating to that fuel up instance or anything else you wish to add. I used it when Winter hit, and will use it to note when my oil changes, etc were done. They are not going to be a part of the vehicle costs on the page though, just notes.
If I put in an additive I just figure the amount, such as if I add a 16 oz bottle of fuel injector cleaner that would be .125 gallons and just add that amount to the gas fillup. So if I actually put 10.125 gallons of gas in and a 16 oz bottle of additive, I'd put the total fill at 10.25 gallons. I know that doesn't make your costs exact, but close. To get the decimal part of a gallon you are adding just divide the number of onces by 128 (number of ounces per gallon) and it converts ounces to decimal gallons.
Its funny, my last fillup I did put in a bottle of injector cleaner.. LOL But I don't see a need to count that among the fuel really. I see where you are going with it, but I think that is being a bit overkill. Most people don't bother with additives since most of them are not truly beneficial anyway. The only reason I put in some injector cleaner is because it needed it, not because I wanted to. I can count the number of times I have used it on my vehicles since I have been driving on less than 2 hands. The 03 van I bought was poorly maintained by the previous owner and needs more work yet, but getting better..
Anyways, not to get off topic. Do you factor in the COST of the additive and add that to your fuel purchase at the time of fillup, including the tax? That would also change your price factor. So in your case, you would put in the additive, then put in the fuel. Later sit down and do some math. You would have to figure your total volume, when you have done, and then your total fuel cost. Since you also have to add in the additive, add the cost of that, plus the tax for it, plus what your fillup was, then divide by the total number of gallons including the additive volume and it will give you a correct per gallon price, leading to a correct cost for that tank.
Though just a thought. Additives are for things like spark knock, or injector cleaning. Do you have spark knock? If so, go up one grade of gas (87 to 89 for example) instead, it will be cheaper. If you are using it for injector cleaning, realistically you should only need that at most every 15-25 thousand miles, or at least once a year. If your injectors are getting THAT dirty to need it each fuel up or something, its time to get gas elsewhere or have your fuel system checked.
Wow, I never knew people took it that seriously I guess I can understand where you're coming from with this....to get the "exact" fill per se that was filled into your vehicle, but even so, it's nearly impossible to ensure a "complete" and accurate fill, unless you take the vehicle to a complete empty tank, and then fill up the tank at the side of the road with a couple gas cans But toting all that gas around could be dangerous.
But yea, I'm with DTMAce, you shouldn't need these additives more than once a year....I generally add a can of Berryman's B-12 CHEMTOOL once or twice a year, right before my planned oil change (there's some theory that the concoction could actually leak past the rings if not burned evenly, and then get trapped in the oil, dilluting/contaminating your oil...which wouldn't be good for a long period of time).
But in a way, I can understand what the OP is asking, a seperate field for "additive price" so the site could compute the additive price in with the fuel price?