[1952henry]

Oxalic acid, which was used as radiator flush from GM, apparently discontinued. Available in hardware stores as wood bleach. Check the label, not all wood bleaches have it as an ingredient. From what I have read, 1/2 -3/4 cup per gallon. Either drive car for an hour or so or let in radiator for a few days. This is followed by a baking or washing soda rinse to neutralize acid.