I didnt want to get the flush all thru the system.My boat was in the water and a supply of good clean fresh water isnt available to flush the cleaner out where I am.I can remove the heat exchanger core on my Deere in about 15 minutes,so that was the easiest way.I think if you flushed the entire system it would clean out everything,block ,coolers,heaters and whatever else.I have heard of alot of scale being loosened up when flushing systems,but that was on older 3208's.I also always find barnacles and seaweed on the sea water side of the core.Old zincs also find thier way to the core. The manual says to rod the core with a 3/16 th brass rod. If you decide to run the cleaner thru the system,you must remove your thermostats.Me and my son both had the same engine,one with green coolant with fleetgaurd DCA additve and the other with premixed rotella.I cleaned both with sizzle acid,and the acid wouldnt touch the rotella,but cleaned the other one perfect as always.That was when I contacted Shell,and they recommended the Prestone flush.I have always just had a 5 gal bucket of sizzle that is used to clean furnaces,that I submerge the core in and then blast it off with a pressure washer.I have been told that a radiator shop that has a tank can clean the core as well.