Using a garden hose to into the Radiator, will it flush out coolant from the Heater core as well?

 

If you set the temperature slider all the way on hot then yes it should. But I'd just disconnect the heater core hoses and flush it on it's own too, that way you can flush it backwards and forwards to clean it out better.

 

"Set the slider all the way on hot"? Is this with the engine on idle or not on idle?

 

if you want to completely remove all the coolant, loosen and remove the drain bolt behind the header. That will drain all the coolant inside the block as well.

 

The slider is connected to a cable that's connected to a valve sticking out of the firewall. When this valve is open coolant can flow into the heater core.

Just go look at the coolant flush instructions in the service manual. That will explain it better than I can.