This is not quite Blazer related but could still apply. I'm working on a GM 3.8 that has random detonation at idle. This is the supercharged engine which makes it all the more prone to detonation. So far I've tracked down some coolant leaks from some elbows. Anyway, there is a small amount of black slime that forms on the bottom of the radiator cap and I assume this is from antifreeze contacting small hot spots in the heads. My main question is if anyone knows what happens to ethylene glycol when it would be heated to boiling point? I've looked up that it is around 370 degrees which seems possible but I'm just not sure if it turns black and gets thick.
Any help would be great. No it is not oil or from a bad head gasket.

 

Let's add to more unanswered posts here in the lounge. I'm pulling the power steering pump and the pulley is stuck. I'll be trying heat next time I'm in the garage but I really liked the pulley on the above mentioned car because it has holes in the pulley so the pump can be removed without taking off the pulley first. Why are all the pulleys not made like this? When I get it out the pulley is going on the mill so I can cut some holes in it. If all goes well I have a few other vehicles to do it to. As long as I make 2 holes it should be balanced. The FWD pulley is a smaller inside diameter though or I would just try to use it instead.