When the engine is warmed up, feel the two heater hoses. If they're too hot to hold onto for very long, (normal), suspect a problem with the temperature door or actuator, or more likely, the heater computer that controls it.
If the hoses are cool, suspect a plugged heater core. They can usually be back flushed with a garden hose.
For engine overheating, if this does not occur at highway speeds, suspect a radiator fan not turning on.
If both symptoms started at the same time, the thermostat was not the problem. During overheating, the air from the heater would have been too hot, not too cold. The two symptoms together suggest coolant is not circulating. Two possible causes are water pump problems or air pockets from a leaking head gasket. Bubbling in the overflow reservoir is a good sign of a head gasket problem. Your mechanic will check at the reservoir with a glass tube filled with a special dark blue liquid that will turn bright yellow if combustion gases are present.
Sunday, January 17th, 2010 AT 8:02 AM