Originally Posted by NaeKuh
improper / insufficient / over rincing...
the vinegar will speed up oxidation inside your rad if you dont properly rince it out, and you'll be back at one.
Of course it will its acidic, if you rinse it a couple of times with hot water its NP, 10% is just enough to kill bacteria and shine the copper up a little. I still use 100% white in old rads and HC's and just leave it a couple of hours and rinse a bunch of times and have never had a problem with it. Or CLR if its really nasty..
10% white, 90% distilled and leave it in the rad over night followed by a lot of hot water rinses then a final fill up with rubbing alcohol to get any machining oils out.