Anytime you flush a cooling system, the heater core needs to be flushed. No matter why you're doing it.
What's the heater core and "raideator", what ever that is, have anything to do with a blown head-gasket? Unfortunately the federal "green" people have taken away powered acid cooling system cleaner.
Yes,
I also recommend taking the radiator to a radiator shop for a professional cleaning, they refer to it as Rodding the core, the radiator tank(s) is removed and rods are used to clean the tubes, after core is placed in cleaner , Then tank is replaced using a new gasket. or if it's the older brass/copper soldered back on...cost is dependent on size of core...
unless there was any debris blocking your old radiator i would say there is nothing to worry about and if so drano works awesome at unclogging heater cores.
Sure, all you have to do is turn the heater on.
Of course!
flush everything that will flush..
