Corrected entry: The main plot device is the lack of petrol. The Doc has an ice generating machine and lamp oil. The ice-generating machine is steam driven and works at ambient temperature. Therefore it is fair to assume that it uses pressure transformation to achieve freezing. It should be fairly simple to rebuild the compression equipment from the icebox into a small scale cracking unit. The required technology is similar. Cracking is the process of breaking down heavy oils like lamp to light ones like petrol. At this point in the film they have several days which should be plenty of time to do this. This would be a much safer course of action.
Corrected entry: During the final train sequence, how does that gauge in the Delorean measure the pressure inside the train, when nothing is physically attached between it and the Delorean to measure that?
Corrected entry: As per http://www.bartleby.com/65/in/intern-co.html, J. J. É. Lenoir built the first gasoline powered internal combustion in 1859. De Rochas patented a design in 1862, and Otto built an engine in 1878. Gottlieb Daimler built what is considered the ancestor of today's internal combustion Engine in 1885. All this is by way of saying that gasoline would not have been impossible to find in 1885...especially considering that Edmund Drake drilled America's first oil well in 1859.
Corrected entry: When the DeLorean suddenly appeared in 1885, the Indians have absolutely no reaction at all. There is no possible way that they wouldn't have been the least bit spooked or confused, and we should have seen some semblance of this in their actions, but they just keep charging on like nothing happened. It'd be like a an alien spaceship appearing out of nowhere in Times Square and people not even batting an eyelash.
Corrected entry: In 1885 Marty meets his great-great-grandparents. His great-great-grandfather looks like him so that we can be sure of their relation. BUT, his great-great-grandmother looks like his own mother. This makes no sense as in this way his parents are related by blood due to the resemblance of their ancestors.
Corrected entry: At the very end of the movie when Marty and Jennifer are at the wreck on the train tracks, the thing starts dinging and the arms lower, indicating that a train is coming. But if Doc is coming from somewhere else in time, then it wouldn't say a train was coming, and one dosn't come later.