Weirdest damage I've ever seen to an engine from catastrophic overheating... a Cherokee 4.0 owner had overheated and kept driving till it was almost glowing, and wouldn't run anymore. I found compression on the cylinders, in order from 1 to 6, to be 0psi, 20psi, 40psi, 60psi, 80psi, and 100psi. Exactly those numbers, as if the head gasket had started melting away perfectly from front to back. Bizarre. Guy towed it away so I never got to see what exactly happened.