Some GM 4.3L engines, which may've been used in the Blazer, where suspectible to problems with Dex-Cool in situations involving low coolant levels. Apparently, when the coolant level is slightly low, some parts of the engine may not be covered with fluid and would rust. The fluid would then wash over these parts at some point and cause "rust dust" or the coolant to turn color. The rust dust could also be the remains of the GM cooling system sealer pellets, but unlikely.
Dex-Cool is supposed to be flushed and filled every 5 years. For me, I try to do it every 3 years.
I'd drain the block (if possible) and the radiator and refill with distilled water (or perhaps tap water if its VERY good in your area). Set the heater on high and start the engine. Allow it to idle until the cooling fan cycles TWICE. Then, drain the flush water and repeat the water flushing process for an additional time. I'd only use the flush additive if the system does not appear clean after two water flushes, but I think you'll be fine.
I just bought some Prestone All Makes/Models antifreeze at Walmart today for less than $9/gal. I personally don't understand why you or I should spend an additional 1/3 for Zerex G-05 or the licensed version of Dex-Cool. The yellow jug Prestone All Makes/Models is nearly identical (if not identical) to the silver jug Prestone Extended life 5/150, with the exception of the orange dye and official GM approval. After refilling, some people have used the GM cooling system pellets as a form of insurance against leaks..but I wouldn't add it unless the engine of yours is known to have leak problems (don't know anything about Blazers). I for one, will not be adding any to the Saturn unless the coolant level begins dropping again.
