Dex-Cool was not intended for use in vehicles with cast iron blocks/heads. It also seems that acids are formed if the system is not completely filled, with no air at all in the radiator. If the system ever overheats, acids are prone to develop due to the chemistry of the coolant at high temperature. Plain old green ethylene glycol is probably the best choice for cast iron engines with copper radiators. Aluminum block/aluminum radiator systems with puke tanks and high-pressure radiator caps that keep the air purged out is what Dex-Cool was designed to be used with, and it seems that idea was only partially successful.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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