Recently in my newest 1992 Volvo 940 GL, the motor overheated on a long bridge in very slow 5 pm traffic. I managed to get to a parking lot in time before the temp gauge hit the red. I opened the hood and the motor was extremely hot and some antifreeze was dripping slowly from the filler tank. I waited for about 1 1/2 hours before turning the car back on and made it back home without reoccurrance. I don't recall hearing the electric fan motor for the radiator/car motor turn on. Is there a sensor for this electric motor that is malfunctioning? How do I test this theory?