Question: How did the new gauge in the car read the boiler temperature? It wasn't connected to the train at all.
Answer: It was based on the speed the train, and therefore the car, was travelling.
Question: Considering what happened with Old Biff and the Almanac in 2015, why did Doc not bother to ask Marty about the whereabouts of the DeLorean upon returning to 1985 in the train? Wouldn't he want to make sure it wouldn't fall into the wrong hands again? I mean he can see a bit of debris when he leans out the window, but that could have fallen off a passing scrap metal train or anything.
Answer: He's already been to the future, so it's possible (probable, even) that he spoke to Marty then and found out that the DeLorean had been destroyed in 1985.
Answer: Many people theorized that since Doc technically was the one that told Marty what time enter on the keypad as when they would arrive in 1985. It's plausible that Doc had planned the DeLorean to be destroyed by the train when they arrived. Remember the original plan was for Doc and Marty to go back together but then Clara showed up and complicated the plan (again). It's quite possible that when they arrived together in 1985 Doc would have warned Marty what was about to happen and they would exited the car long beforehand then to witness the DeLorean's destruction.
Answer: There was actually much debris (the entire car) around the track that Doc surveys as soon as he arrives with the time-travel train. He'd know better than anyone that it was the DeLorean, particularly as he planned his arrival for just a few minutes behind when Marty arrived back in 1985. Marty couldn't have done anything with the DeLorean in such a short amount of time.
Question: After deciding not to race Needles, Jennifer looks at the fax that she took from 2015 and sees that the words "YOU'RE FIRED!" were erased. Why didn't the name of the company also get erased?
Answer: The company would still be in the future, Marty wouldn't be working for it. His career as a musician would have taken off.
Question: Just wanting to know about the animal running in front of the Native Americans when Marty travels back to 1885. Looks like a dog, but was it meant to be there, or was it an animal that was disturbed as they did the scene and it bolted for its life?
Answer: It is a rabbit that probably got disturbed by the filming.
Answer: Steam, the whole thing is steam powered. He has just modified the train itself, probably making it much more efficient.
David Mercier