Loco operating practices in icy winter

Here's a query that came up when thinking about what engine crews must have had to deal with in winter, other than the obvious physical confort issues. Maybe some of you operators can share your thoughts.

In well-below-freezing conditions, exactly how would your practices or precautions change to avoid operating problems on the road? For example, what about water trapped in air systems? Was it necessary to change firing practices or did engine "efficiency" change noticably?

I'm aware that there were means to introduce steam heat to the tenders (always?). But what glitches could happen with feedwater systems?

That's a lot of questions . . . thanks in advance for sharing you answers.

Bob of AZ