The radiator may be full of "muck" (for lack of a technical term) and when the deposits form on the inside of the radiator, they block thermal conductivity. If this is the case, it may call for replacement of the radiator. To bleed the cooling system, open the screw on top of the thermostat housing and fill the system until there is a steady stream from the pee hole, then close the screw and top off the coolant, start the car and turn the heater to hot and idle the engine until operating temperature is achieved. Let cool and recheck coolant level.
Monday, April 13th, 2009 AT 12:33 PM