Suggestion: Table to enter multiple fillups ala Profile listing
 

Would be nice to have a table - rows of empty cells - to fill in multiple fillups quickly.

Laid out like how the past fillups are listed on the car's profile page.

Take a look at importing fuel-ups. You can use a program like Notepad to put together a simple file with all of your fuel-ups and add them all at once. That should be even easier than a bunch of forms on a web page.

And if Notepad is too free-form, you could use something like Excel to enter all the values and then save that file as a text-only CSV.