may be a temp switch, or an open circut you if the car is not acually running hot then it should be ok to drive it, but dont travel to far to fast in case they are lieying you going to want to take it back to a dealer or some place that knows what the hell they are doing. a dealer will stand behind what they do a independant dosnt. take it back to the first dealer and tell them this is what has happend since you replaced the radiator. try that.