If I were a betting man…wait, I most definitely am…I’d wager $100 that your trouble is with the intake gaskets and not the radiator.
a compression test can point to head gaskets, cracked block. what can I do to verify a blown lower intake manifold gasket.
Open it up, and it will show itself.
Dexcool in and of itself is not a problem, if it’s changed every 5 years. Obviously, most people don’t do this, and that’s when Dexcool becomes a problem
However, any degraded coolant can become a problem
As for that nasty stuff in the radiator, I’ve seen that at work also. I tend to service the dexcool in our GM fleet vehicles every 5 years. But my colleagues don’t always do this. The ones with the nasty radiators are usually the ones that have been neglected
I would concentrate on the lower intake gaskets and forget about the radiator
It wouldn’t hurt to flush out the radiator with hot water until it runs clear
I’m going to say something now which some of the others will vehemently and violently disagree with . . . use a 50/50 mix of Dexcool and distilled water. Because that’s what your vehicle is designed to use. As I said, if you service the Dexcool every 5 years, it’s not a problem. But if your system’s already messed up from previous neglect, switching to a different coolant will not make those problems disappear