Why couldn’t Doc just make his own gasoline?
Doc who knows how to make a time machine and despite how back in antiquity he went, he was able to create an ice-cube machine. By that logic, can we assume that Doc can easily create a time machine? The problem in 1885 was of course, that there’s no gasoline to fuel the DeLorean.
But since Doc should’ve known more, wouldn’t he then know that kerosene was available in 1885? Couldn't he simply track down where kerosene was being refined to make some gasoline off the by-product of that process?