Big Steam trips

With regards to the big steam trips that operate on the mainline with a backup Amtrak P42, (like MILW 261) is the diesel isolated or running in kind of a poor-man's MU (via radio)? I've seen some youtube vids of 261, and it sounds like the diesel is just idling.

Just to judge by the sound when I have seen it, it is running no more than it needs to in order to provide the HEP for the consist. When the UP operates their steamers, there is a converted freight car in the consist to provide the HEP. The last time I saw them, UPP 9326 was providing the power, but they probably have more than one power car.

Often times the diesels are there to provide dynamic braking (on runs with heavy grades) and as protection power in case anything happens with the steamer, so that the train can get cleared up into a siding and not foul a busy main.

Larger steamers like the UP's duo and NS's now cold 611 and 1218 had/have no trouble with 15-20 car consists under most circumstances.

In the early 1990's (can't remember which year), Atlanta & West Point 290 (a heavy 4-6-2) subbed for NS's 611 & 1218, neither of which were ready for an early NS trip out of Jacksonville. The 290 came with a pair of New Georgia F units behind it. The steam crew commented that the (I think) 18 car consist was no trouble for the 290, aside from needing a short boost from the F's to get it rolling, but that it kept it at speed all on its own.