Many mountain hikers recommend drinking hot fluids, because they provide a lot of energy. According to the discussion "Does eating snow help dehydration?", the actual calorie gain is minimal, however there are calories available practically immediately.
However, how hot can water/fluid be to be able to safely drink it (how many degrees)? Too hot water would burn your lips, but if the water is not hot enough to burn the lips, is it safe to swallow? Does the large amount of hot fluid in the stomach pose any threat to the body, or I can assume that anything I can swallow without getting burned is safe for me?