1996 cobra runs hot. fan not coming on at 200 degrees. if I unplug from the fan at the sensor the fan comes on. the sensor is new. the thermostat is new and also new 3 row alum radiator. I started to burp the air at the crossover and notice constant air bubbling at the crossover in a funnel filled with antifreeze. rev the engine and the bubbles increase. Head gasket???