You already know that throwing parts at a car is not healthy for you or your pocket, now you already know that there are test on the cooling system that can also be done,(before buying so many not working parts).. But from your stand point, i would like to ask first have you seen any antifreeze leakages?,around any cooling system parts, a visual inspection is the first action that you want to perform, then when the vehicle was running hot as it cools down a safe smell test, looking closely at the following areas, temperature sensor, small leaks or cracks in your upper and lower hoses. make sure you arent using water only in cold conditions, recheck all new/used parts you have changed, also i know it may be hard to see the water pump, this is where cooling system pressure test come in, Is there a large amounts of white smoke comming from the tail pipe? check oil dipstick for signs of antifreeze and oil mixing,(this is a big problem head gasket)oil will look milky, has the fan been checked for operation, have you seen or heard the cooling fan come on when you were driving? When a cooling fan will not operate it can be due to a bad relay,or wire/connector,bad fan motor, now the relay is normally in the fuse box under the hood.Is the correct amount of coolant in the vehicle? Remember something cause this car to run hot, Has your check engine light come on, if so a code may have set, and diagnostics may be needed, By the way you are calling the radiator "used, is the thermostate used also, if so this means that possibly the orginal one you removed could be good, used parts are good sometime, but unless the part has been checked you are taking a chance, and when dealing with the cooling system you so want to try and use NEW parts. When you put the used parts on did you bleed the cooling system of excess air? Are you a DIYer?. At this point you may need to go to the professionals for some of the above recommendations, its ok when and if you go ask plenty questions,learning automotives is good. I also dont want to leave out a bad core plug.Also was the used radiator clean of all corrosion and rust build up?