Quote Originally Posted by Waterlogged View Post
Go with distilled white vinegar if you go that route. Personally, I wouldn't go longer than 15 min soak and then that would be followed by liberal flushing with distilled/demin water. Do the rad just before you install it and fill the loop ASAP afterwards, so it doesn't get a chance to start oxidizing inside.
I have a PA120.2 that I filled with vinegar and let it sit for about 10 hours, periodically I would run hot water through the fins to heat the thing up. It got the PC ice gunk that was in it out finally without detriment to the radiator and is working fine about a year later.