I have used wood bleach (oxalic acid that used to be Prestone radiator flush, and washing soda, not baking soda to neutralize). I ran my model A for a summer with water wetter and plain water. Big mistake ,huge rust in the block.
Here is a long complicated post about this cleaner.
http://forums.corvetteforum.com/c3-t...ner-flush.html
9 dry oz of Oxalic Acid (DAP Wood Bleach)
2 dry oz of Sodium Carbonate (Arm & Hammer Super Washing Soda)
Mix acid with water in a bucket,pour in and idle untill up to temperature and leave in for a couple of hours. Neutralize with washing soda. This took all the rust out of my block and it does not attack any good metal.
This stuff really works. Here is a thread on HAMB. Doesn't even harm paint.
http://www.jalopyjournal.com/forum/s...ht=oxalic+acid
John