And just in case anyone thinks to ask why, when Marty is stuck in 1885 in BTTF III after all the fuel leaks out of his version of the car, he doesn't siphon gas from the version of the car that is stored in the mine. Two things about that:
- Marty wouldn't want to risk damaging the version of the car that's buried in the mine, because he will one day have to unearth it in 1955. In fact, he's already done this, because he wouldn't even be able to get to 1885 if he hadn't. So logically speaking he can't do anything to change that.
- There wouldn't BE any gas in the car when Doc buries in in the mine, because everyone knows you have to drain all the fluids when you store a car for extended periods of time.