check to see if your radiator fan is working. I expect your temperature gauge is Hot so your fans should be running. if the radiator fan isn't running, then that's why the radiator is overheating and boiling over.
if you have air conditioning in the car, turn that on. that should turn on the condensor fan and that will cool the radiator if the radiator fan isn't working. that is assuming that the air conditioning fan works. that afan should come on anytime the air conditioning is on.
also, if the fan is working, then you need to bleed the air out of the cooling system. there should be a bleed screw on the thermostat housing to let the air out. if air is trapped in the system then the coolant can't circulate and that will cause the boil over.
if the radiator fan isn't working, it could be the fan motor, the temp sensor or the radiator relay that isn't functional.
hope that helps
