Join Date: Aug 2018
Location: Fort Worth, Texas, USA
As I remember when I used it, yes, it is normal to turn blackish and to stink. That happens when it is bonding to the iron particulates. You need to flush that stuff out of the block's passageways like EvenFlow suggested.
For confirmation, read some of the comments:
As others have said it smells awful when you drain it, and if your system is as bad as mine it may come out as a sludge. I had to do both a hose flush and run 20 gallons of distilled through after to clear everything out. (Summit Racing)
Using this flush did produce a black grungy color and many small black particles with the smell of rotten eggs. Not sure if this was a reaction to rust or not. One caution is don't only do two, after use flushes, as is in the instructions, you will still be left with black-ish grunge in the coolant after running the car for a time. I had to re-drain and flush with a garden hose a lot, thereby wasting new anti-freeze, to get to clear coolant. (Amazon)
Build Date: July 18, 1966