cherrybim, actually, many poeple serve coffee (or tea) that is not necessarily piping hot…many people let the coffee cool a bit…so your question can be answered easily. When I have to make havdalah on coffee, I put a fair amount of milk into it to cool it.
I still fail to see the difference between tea and coffee as per it being called water. BOTH are water with an infusion of a taste- tea leaves or coffee beans.
And, clearly, if you accept Rav Ruderman’s psak, then tea and coffee are surely OK.
BTW- you keep on writing about havdalah- the same will go for kiddush in the morning,called kuddusha rabbah, when ‘chamar medinah’ is OK.