I think I owe AF a post because it was so helpful...
I bought a 2003 Impala with the 3800 series engine and 135K miles a couple of months ago in November 2016... it started overheating at lights and I thought it was low on radiator fluid so I went to top it off and shocked to feel a slimy sludge on the neck and cap. First thing I thought was bad head gasket and checked the oil... it wasn't solid black but not chocolate mile either... bought some headgasket repair liquid and it said to flush thoroughly fist... so I bought a cheap flush... drained it and noticed a purple tint to the radiator fluid... I'm use to seeing green... thought that odd... flushed it twice before the final step of adding the flush.
Just plain ole tap water... the car has been running cool as a cucumber since! NOW I'm thinking of returning the headgasket repair liquid...
BUT... the point of the story is this... I started seeing all this stuff on many different sites about something called Dex Cool.... NEVER heard of it before....
DEXCOOL is very... VERY bad!