mostly is head gasket leak, bad thermostat, clogged radiator , leak in the cooling system, buy block tester to see if your head gasket is leaking..check your oil cover for milky white appearance like spoiled milk, white misty smoke from cold engine start on your muffler and rough idle during cold start which last for a seconds to a minute.
How hot? What does the temp guage show? Do you see any leaks or puddles on the ground after you park it and return to the vehicle? Do you smell coolant when you are outside the vehicle? Which engine do you have in the vehicle (4 or 6 cylinder)?
If it is hitting the red, and you have no leaks, you could have a bad thermostat, a cooling fan issue, or a water pump issue. Take it to a shop and have the system pressure tested to look for leaks, and then, have them check the cooling system with an emissions analyzer probe to see if there are any hydrocarbons in the system. You could have a head gasket issue. Unless you have access to test equipment, the diag won't be a DIY type issue. You could also have a bad temp sensor or Temp Guage issue, but that would be less common.