1999 Honda CRV engine heating

The problem is the "car overheats while climbing hills or long distance". There could be any of a dozen different causes. Rather than typing for an hour to cover every possibility, what have you checked so far, or what other clues have you observed? Does running the heater on a high setting bring the temperature down? What is the symptom that tells you the engine is overheating? Do you live in an area where they throw a pound of salt on an ounce of snow? Have you checked the coolant level, and when is the last time it was changed?