1996 Caravan, 2.4, runs fine on open road with no problems. When you get into stop and go traffic, now the problem starts. It wants to start overheating. It will eventually peg the gauge! But before that happens, I turn the heater on, and it kicks the fans in and starts declineing. Does this vehicle have a relay problem or a coolant temperature sensor problem? If it has a relay, where is it located? I know where the sensor is.