Omegaman,

your hypothesis is clever; however, not quite correct. The dump cycle is designed to:
#1 rapidly discharge the load
#2 completely discharge the load.

After years in rail service, I have encountered numerous rail cars returned to my facilities with material remaining in the car (and not from freezing I assure you).

The coal industry survives by VOLUME in every aspect of the operations from extraction, processing, loading, unloading, and delivery. What some may describe as extreme measures are employed to maximize profits and minimize costs on a scale not unlike the automotive industry (and grain) to mention another "efficiency" expert. Imagine shipping out 50Ktons of material each month, and having 10% or more return to you. Somebody didn't get all they paid for. Naturally, for me it was a windfall. I re-sold the material, gaining sales on volume that cost 0 to produce/load. The negative came when I had to unload the remainder since the material contained was not compatible to what was to be loaded and shipped (pool cars, not a lease fleet).

Walgamuth,
You can look at a placard on the side of a railcar (it is usually Black, outlined in white with white lettering). There, you can read the build date, and more importantly, the reblt date. Many cars are "renewed" and appear new, when only the running gear and paint is refreshed... It is kinda a hobby to watch the placards on a slow-moving train at a crossing, and see how old some of the gear actually is.

__________________
RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?