the crockpot and antifreeze does work wonders on all engines ,but on those extreme cases ive also tried crockpot and prestone super antifreeze cleaner duluted to 1/4 cup cleaner to 1 gallon water then cooked overnight on low ( only on those engines i got from yard sales with 30 plus years of corrosion on them and locked up ) they came out clean as a whistle and most were not locked up anymore i only had to wipe away a residue left on the engines then cleaned all with 10 weight oil to displace water , the super radiator cleaner solution should only be used on extreamly corroaded engines which antifreeze alone doesnt do the trick .