Where this idea of the heater core being the problem I can't figure.
Blown head gasket is most likely the cause.
Coolant not returning to the radiator indicates either a bad pressure cap or a leak in the cooling system. If the new cap is good (OEM ones will be, aftermarket ones might be) that means there is a leak somewhere. One place unique to this radiator is the flat spot where the front brace fits over the radiator. It is common for it to develop a crack there and leak enough to produce your symptoms.
Then again, overheating at idle may be the result of a bubble in the coolant. If it was not purged when the coolant was last filled it almost certainly has a bubble. There is a bleed nipple, like an oversized brake bleed nipple, on the housing where the upper radiator hose connects to the engine. With the engine cool, open that nipple half a turn and close it when a steady stream of coolant comes out.
If you do not know "what to do," then, why did you guess and spent money, wasted really, into the parts you purchased? Cars are repaired by experts, by trained mechanics. Are you in fear of mechanics? This is a twenty year old car with probably over 200,000 miles on the worn out engine. You also failed to use proper English grammar preferring to use texting slang code. Neither is advisable. Call a mechanic and learn to write correctly, please.
Probably the heater-core is corroded badly, everyone seems to forget about that the heater-core which is part of the cooling system.
replaced the radiator and thermostat and radiatior cap, but the car keeps pushing the coolant into the overflow tank and car over heats at idle because its pushing all the coolant into the tank and over flowing, checked the lines and its not plugged and coolant wont return to the radiatior I don't know what to do
