Have a well cared for, 2004 xa, 70,000mi. Heat blowing only cool air. Upon inspection of the cooling system we found a waxy build up around the neck of the radiator. Have no idea if this is related to the heat problem. My mechanic, who is also a good friend, has also done some preliminary checking of electrical, switches, and basic troubleshooting. Would welcome any thoughts. Other posts in other forums have suggested that the waxy build up is either a non issue, indication of a blown head gasket, or tranny fluid mixing with coolant.