This is an experiment! I am NOT recommending you do this!! Do At Your Own Risk!!! I Take No Responsibility For Any Damage Or Personal Injury!! How I Cleaned out my Jeep JK heater core with muriatic acid only flushing the heater core and not the whole coolant system...Be careful!!! Here is a link to how change out your heater core with out removing the dash and heater box...
   • Jeep JK Heater Core replacement EASY ...  
I will be changing the core out soon and cut it open and post it here so see if the acid compromised the core at all wait for it before you think about doing this!!