What causes a 96 Chevy lumina to run hot the radiator is full but the water just boils?

There could be several reasons, including the radiator being plugged up, the thermostat being stuck, and the water pump not working. Drain the coolant, and check for signs of rust or corrosion in the coolant. Remove the thermostat, replace the coolant, and run the engine. If the problem persists, take it to garage. Troubleshooting by changing out parts will be too expensive. check and change thermostat if done this problem is either head gasket or cracked head