Why was the tender still attached?

Question

Apart from the opportunity for Clara Clayton to have an exciting traversal of the distance between the back of the fuel tender and the engine (Golly!) in Back to the Future III: Was there any reason to leave the tender attached to the engine?

1. Fully loaded, it would probably weigh half as much as the engine itself. The less mass a surface vehicle is hauling, the quicker it can accelerate.
2. For fuel they were mostly relying on the color coded burn sticks the Doc used in his furnace. Even if they'd needed extra fuel beyond that, they could've stocked the furnace & detached the tender when they stopped for the car. It was not far from there to the point of '88 or bust'.

I don't think I've ever seen a steam engine traveling with no tender. So it might be that a steam train and its tender are effectively inseparable, but I am no train buff.

One might also ponder why the Doc didn't just stuff a long tube full with gunpowder, put a shaped nozzle at one end & call it a solid rocket motor - but perhaps that is for another question.. (starts hummin' to the tune of Rocket 88..)

Answer 1

First question: It's probably been that way for the whole story to work (otherwise they'd just have lost Clara before the Point of No Return - or something like that.

There have indeed been different steam engines, some requiring a tender, some having a small built-in tender (they could use for shorter routes). I can't watch the movie right now, but I'm sure they've had a separate one only (one you could detach).

However, there's another fact you're ignoring: The tender is heavy, yes, but this additional weight also makes the whole train more stable. So I could also think, that - with the tender detached and the improved velocity - the train would no longer run stable and probably even derail. So the whole thing might have been left there intentionally.

To cite the German wikipedia: A useful side effect is the usually heavy tender (fully loaded 50-70 t for Europe or 130-205 t for the US), which will stabilize the often unruly and twitching train, caused by the free mass forces of the engine (especially for trains with two cylinders). Due to this the tender is connected without play, but not fixed." (Few more details in my comments.)

Second question: This might have been out of the question for him (lack of resources and time). After all, they had just a limited timeframe to work with (their primary reason for leaving immediately has been Doc's approaching date of death).