Hose life....

All rubber is cured (via the vulcanizing process invented by Charles Goodyear) and that curing process tends to continue through its life a very slow rate; heat accelerates the curing rate. At it cures more and more, it get harder and harder. So heat will harden any rubber. That's why ties go 'bad' after many years.... or go bad on a race tack very fast if you push them too hard and get them too hot: the rubber hardens up. It's gonna happen with a rad hose too if you actually use the engine and it gets heat to the rubber.

I can't tell you about silicone hoses.....