The exhaust manifold glows blue and eventually cracks.

What is your question?

My cat convertor lasted 10K and turned blue also. I have replaced EVERYTHING several times over (8 manifolds, two cat convertors, o2 sensors, egr valve, etc.) Even replaced the motor with a low mileage used one,11,000 miles ago. Been to several dealers that keep wanting to replace the same parts over and over. This has been going on since I bought the truck at 135,000 miles. Any clues?