It's a great question, and is tough to answer intuitively without speaking a native language that actually has such a word.

I would agree that "boiling milk" and "boiling oil" are very unlikely to get separate words, unless one of them happens to be an extremely common thing that people encounter a lot and that has special practical implications.

Milk might be a special case, in that it essentially is just water with some other stuff dissolved. It is to water as salt water is to water... but more so.

My guess would be that the single word might get pressed into service like "ice" does, but I think we'd have to find languages that include this word and survey native speakers. It could vary.

Nearly everyone encounters boiling water in everyday life, but do most people ever see other liquids boiling, even once, and especially during the historical periods that shaped our current languages? If not we might be getting into something like technical language, where daily life lines up poorly and terms and jargon get formalized.