Too much heat

I have put an IR gun on the exhaust manifolds, and most engines idle at about 300* to 450*F. Running the Rs up just a little can bring the exhaust MANIFOLDS up to 400,500, and more very quickly.So the exhaust itself could be higher. I have read that the combustion chamber temperature can regularly be 800*F and even to 1000 degrees. I don't imagine that crossover getting up that high, obviously. But since the underside of that passage gets coked up, and even the internal crossover cokes up on hi-mileage engines, we can know that it regularly exceeds 250*F. Perhaps it runs over that more or less continuously.
I've never been able to keep paint on there for very long either.