I've used acid to clean some really nasty cooling systems, including a fleet of concrete mixers I maintained. It's important to neutralize the acid by dumping a couple of boxes of baking soda into a fresh water fill after draining the acid wash. Run the soda mix for 10-15 minutes, then flush again with clear water. Refill with a 50/50 antifreeze/water mixture and you're good to go!
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
Love your enemies and drive 'em nuts!