Ok well my gf has a lexus ES300. Her car has smoke comming fom the overflow reseviour* for the coolant. Her coolant is filled to the full mark, so is it just overfilled? That was my initial answer because the temp. guage is fine and the engine isnt overheating. But my only question is that why does the coolant boil in teh reseviour container?
Thanks

 

I think you answered your own question, Overflow reservoir. Sounds like its doing it job. Just to be sure though, you might want to make sure there isn't any air in the lines and make the headgasket doesn't have a small leak into the oil. Also, the water coolant mixture might be off.