The hatches diverted warm air back into the engine room, to keep things working better in the cold. There were a set of louvers/shutters in the hatch; in the summer they would be open for cooling, in the winter closed to heat the engine room.
Some ALCos had all sorts of extra railroad-added ductwork on top to accomplish the same thing.
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com
What was the purpose of the winterization hatches EMD used, and were they used on single radiator fan engines like the RS2 I'm getting?