Question: I have 1996 Chevy Camaro V6 it has sludge in top of the radiator and you can dig it out with your finger. It looks like gobs of grease. Can't figure out where it came from it looks like a bad kidney.
Answer: This is actually a common and almost normal condition with the orange Dexcool antifreeze when it has not been changed in a long time. It develops this sludge. The formula makeup has been changed from what it was the first few years it came out.
It is also possible you have an intake manifold or cylinder head leaking. When combustion gases get into the cooling system, it causes this on the old orange coolant.