Some of you may know Mr. Dirty Coolant as DEX-COOL®. Not cool with 1999 GM Blazers though because it correlates with blocked heater cores caused by intake manifold gasket leaks. Moreover, may still show up with that generation of Vor Tech engines even after you replace your gaskets. You will notice the dirty coolant in the reservoir and radiator and will have to flush more than normal for years so skip your faith with this 100,000 mile coolant unless your thinking cool means no heat literally. Please message me if you are a technician and interested in a specific flush for this vehicle. I have no experience with this aforementioned flush but possess the parts and procedure list from a certified and experienced source.
-- (This post is also on the home page of www.searchautoparts.com which I also blog for under my alias: Ole_Blue).
Comment from Peter:
This has been a problem since 1996. I agree a Quality flush is a "must do". There may also be other contributing conditions, such as a leaky radiator cap. Specifically the outer seal. The coolant level eventually gets low enough to add air into the mix. GM included a radiator cap and thermostat replacement into their 3.6 hour flush procedure 99-06-02-012C on several 1996-1998 vehicles. The bulletin was based on the symptoms for rust, heater blows cold air, engine overheat. The bulletin is limited to just a few vehicles, but as Kerri pointed out, the condition affects quite a few.
It is always a good idea to look for that hidden culprit, or at least contributor while servicing the symptoms to further help avoid recreating the brown mess later.