Replace it.
through a cracked heater core - possible.
its the heater core. but its not clogged. its cracked
Cracked heater core
You have either a cracked heater core or bad heater hoses that are allowing antifreeze to enter into the vehicle............
could be a cracked radiator, bad radiator cap, a busted radiator or heater hose, bad heater core, or a busted fill box!
If it is frozen it probably cracked and will leak when thawed. Only way I know is to put in a warm area, garage, etc.
Begin by removing the water supply hoses to your heater core. Remove the heater core retaining bolts. The heater core will come out. Reverse the process to install the new heater core.
the heater core, heater core hoses or heater control valve is leaking
Remove the water supply hoses from your 1985 Chevy heater core. Remove the heater core retaining bolts. The heater core will come out. Reverse the process to install your new heater core.
You can access the heater core from the passenger side kick plate in your 1964 Chevrolet Corvette. Remove the heater core water supply hoses. Remove the heater core retaining bolts. The heater core will come out.
The heater coil and a heater core is the same thing. Hot water circulates from the engine and through the heater core then back to engine generating heat for your heater system.
The heater matrix, in a Peugeot 206, can be replaced by removing the heater core and the hoses. With the heater core removed you can replace it with a new heater core.