I've been having some cooling problems the last 2 weeks. My cooling fan was burnt, and had to be replaced last week. I drove for a week, and now I'm out of anti-freeze again and the car started overheating. I attempted to drive to my mechanic the next day when the engine was cool. The heater core tube is disintegrated, and releasing white smoke from under the hood. I really didn't drive that far when the engine was over-heating, I pulled over, and waited for it to cool down. My mechanic will repair the heater core tube today. 'But if the engine keeps knocking after, what could the problem be? After reading a bunch of threads I'm pretty worried about the head gaskets. To my knowledge there is NO white smoke coming from the exhaust. The car didn't overheat passed the N on the temperature gauge. If anything it peaked between N and O.