Buzz,the engine came from the Kanas City area,was in an old church bus.Must have been a poor congregation, couldn't afford proper coolant
The hot tank has a lye solution,pretty much takes care of rust,but not heavy mineral deposits,they need to be mechanically removed.A long screw driver poked down through coolant passage holes in the block deck helped loosen the mess too.
Stovebold,I've used phrosphoric acid before,also used Muriatic(sulfuric) acid to clean mineral deposits . The cleaning process mentioned by the machine shop is done by "baking" the block and seems to involve something more hi tech than acid alone.
