On the Buick, make absolutely sure to flush the system out to remove as much of the Dex-cool as you can. When Dex-Cool mixes with old school green antifreeze, nasty things can happen. At best, it'll just sludge up and make a slimy brown mess. At worst, and I have seen this happen, it'll set up link concrete in the cooling passages. If you do change it over, I would suggest using the "mix with any", which is the Chrysler spec HOAT, and is a greenish-gold in color. Much better than Dex-Cool, works fine in old school systems, too. I've been running that in mine without any problems at all.
