A few months ago my truck was over heating and I ended up having to have the radiator boiled out and cleaned and I haven't had a problem since until today. My gauges were reading hot and my heat would go cold as the gauge would get higher. It would get to the far right then go back down to normal then the heat would get warm again. Then the gauge would start climbng and the heat would go cold again and when I got to work I could smell antifreeze. I don't know what the problem could be since I had the radiator cleaned completely this past fall. Also when my truck sits idle wiu the defrost going; itnever gets warm and keeps blowing cold air. Any help would be appreciated.

02 chevy blazer automatic 120000 miles

 

Start with flushing the heater core both directions and purging air from the coolant system.

Disconnect both hoses to the heater core on the outside of the firewall. Connect a garden hose to the inlet and run water through until it comes out clear. Repeat the procedure for the outlet to the core.
To purge air raise the front of the vehicle with the passenger side slightly higher remove the radiator cap and run the engine to operating temperature watching for air bubbles at the filler neck. Add coolant as needed let the engine cool and repeat procedure. Possibly a third cycle.

 

x2 on the flush
look into getting a new thermostat too, if its never had a new one put in