Sean and Troy R are right, and Troy R is especially right that thermostats almost never cause overheating. I have only seen it twice in my life and it is unmistakable: the upper radiator hose stays completely cold and the engine overheats controllably in less than 5 minutes.

If it is getting hot and staying hot the radiator is very likely to blame... especially if tap water has ever been added to dilute coolant. The hard water minerals build up in the tubes, where the water cools, and fills the tubes with limestone. I have had a used car that had the bottom third of the radiator tubes blocked solid after a single coolant change that included a gallon of tap water.

Follow the top radiator hose the housing has 2 bolts remove the hose from the housing then remove the 2 bolts that hold the housing remove thermostat. To test the thermostat drop it i a pot of water turn burner on high and when water gets hot 165-185 degrees it will open then you will know if it is good or bad. That motor has a clutch fan is it working proper? Also before you remove and test the thermostat take the radiator cap off and let the engine warm up you can look and see the water flowing in the radiator witch means the thermostat is working

Follow the large top radiator hose to the intake manifold. It's under the piece the radiator hose is clamped to. In 25 + years of wrenching I've only seen 1 thermostat stick closed. It's summer time , just take the thermostat out, if it still overheats then it's not the problem .

You at least need a gasket before you take it apart. You can run without one temporarily if need be.

Make sure you don't put the new one in backwards " the spring goes toward the engine"

Follow the water hose pump that will lead you to the thermostat

I own a 1984 caprice it has the 5.0 liter 305 v8 and is over heating. Aftet checking with parents amd my friend who is a mechanic we all agree the thermostat is stuck. Im going to replace it but i cant find it. I cant find diagrams, i cant find help anywhere. I followed my top radiator hose to the block and about the time i got to my air filter i hit a tangle of more hoses i see what might be the housing but its deep in and blocked by my air filter's housing. Also i am not proficient in my engine parts ill need visual descriptions of it, im not positive if i followed the correct hose it was coming out of the right side of the radiator and it was higher than the rest and very thick. Help would be MUCH appreciated i have a trip i need to make tomorrow...