Radiator could be plugged but a leaking head gasket would be more common. If you see that boiling right after the engine is started and obviously not warmed up yet, suspect the head gasket. The clue is there won't be any steam associated with that bubbling. The air will form a pocket under the thermostat and prevent it from opening. Thermostats open in response to hot liquid, not hot air.
Your mechanic can perform a "sniffer" test to check for a leaking head gasket. Air is drawn from the radiator or reservoir through a glass cylinder with two chambers partially filled with a special dark blue liquid. If combustion gases are present, that liquid will turn bright yellow.
Tuesday, January 17th, 2012 AT 4:57 PM