My 2010 Mazda3 heater control dial has never worked. The heat is HOT only not going down at all when you turn the dial down. Dealer (which was closer to my home) took dash out and replaced heater blender box doors which did nothing. Car has strong smell of coolant after this which it never had before. Returned to dealer twice who kept for a week and did no repair to. Coolant smell is getting worse. This dealer stated that Mazda said uncontrollable hot heat is normal and all Mazda 3s operate this way but customer service Mazda told me I should be able to turn down heat. My 2006 Mazda3 never had this problem. Any thoughts?