Are you sure its the radiator as it could be the thermostat, water pump, or the radiator.

Remove the radiator cap and check the condition of the water, if its not got anti freeze in it will corrode the waterways inside the engine and this can cause overheating. If its sludgy drain the water and flush with a hosepipe until its clean, remove and test the thermostat with a pan of boiling water, and remoce the drive belts and test the waterpump for play or noise in the bearings. Also check the radiator cap for spring tension and its rubber seal is undamaged.