Back when I did the block-seal-in-a-can fix for the 2nd time, I noticed that my once mighty heater-'o-death had been reduced to a simpering lukewarm unit totally unsuited for its purpose. I assume I just plugged the damned thing up with the sealer.

I am curious about the logic of the heater. Specifically, how does the heater core work, how does the 'flow' of the coolant circuit the system? My car's engine blew 2 years ago, in January. I know that the heater was on (for what is was worth) and the control **** is still in the 'max-hot' position.
The other day I blew thru the hose going into the heater core (passenger side hose coming from engine), expecting it to be plugged, however it obediently gurgled out the hose that ends up coming out of the driver's side.
Is it possible the core is indeed plugged and the coolant is simply bypassing the core-matrix? Or is it more complex than that now, with no power to the unit? Perhaps some electrically controlled valve is shut off?

 

the core is just a mini radiator under the dash. With the control on "cool", it blocks the coolant from entering the core (and being returned to the engine). With it on hot, the valve is opened, the radiator gets hot, and the fan blows the hot air inside.

Many people report cores get clogged after time when using the block seal stuff. Since you reoprt hot coolant getting to the core via the hoses, it sounds like your core is just all plugged up. (IMHO).

 

Just get rid of the damn thing. Pull it out and put a line in it's place. You shouldn't drive your FD in the winter anyways.