Depending on where the crack is, it can be fixed. I had a cracked cast exhaust manifold in a bolt hole location and tried a few welding solutions. The fancy nickel .030 MIG wire did not work (did not stick to parent iron). Ended up using regular mild steel .024 without pre heating. Grind the crack, hit a dot of MIG, let cool, grind. Repeat until crack is filled
I was able to torque it down without any cracking, but have not tried a heat cycle yet. Just my .02
