98 sunfire gt overheating

My 98 sunfire with over 100k miles has been overheating lately. It runs real hot then I crank on the heater to cool it down but its just too hot in florida to be doing this. It seems like sometimes it will be overheating then drop down to normal real fast like the fan isnt working all the time for some reason. I have put coolant in there before because it was low but lately I havent needed any or noticed any leaks or anything. Any suggestions what's going on here?

It sounds like the thermostat is sticking closed and then opening all at once. Replace it for a few bucks. Also check the fan relay, it could be going bad or the temp sensor for the fans is shot and not allowing them to come on at the correct time. You should be able to see if there is a problem with the fans themselves by turning the AC on as the fans should run all the time. If they don't come on then you may have to replace the fans themselves.