I can tell you what I did. I dumped the entire cooling system, refilled with tap water ran it couple miles, drained it, refilled with water and cooling system cleaner and drove it for a month. Then i drained it, filled with water, ran a little bit, drained it, refilled water again, ran again, drained, then I took my air hose and blew out the heater core and radiator and made sure nothing was left in it. Every time I did this I watched what came out of the block drains. Last time was clean, so I closed everything up and filled it with final charge. 2 years it still looks new. Maybe a little extreme but my cooling system was neglected so I wanted it clean.