My car gives smoke( steam?) from underneath the radiator when heater is on . A/C works fine, without any smoke.If heater core leaks, shouldn't the steam come from closer to the hood?coolant level reduces with heater,not with A/c.Where could the leak be? Thnx

 

The heater core is located on the interior side of the firewall. If it was leaking, you would have coolant on you're carpet. I dont understand why its only steaming when the heater is on. Did you check the lower hose? Or the radiator itself?

 

When my heater core blew I would have this almost clear color smoke with the nastiest smell leak out from under my hood.

 

Stock radiator ends are plastic and over time can crack. My guess is that you have a small crack in the bottom of your radiator.

 

Check the coolant lines that run to the heater core(the ones that run into the firewall on the passenger side) for leaks.