exhaust manifold cracked

[dan313]

What would cause an exaust mamifold to crack. I was told this by my mechanic because i had water entering 4 out of 8 cylinders of the motor.
He changed one side and ran the boat. He said it checked ok. I'm picking it up tomorrow. Any ideas?????

 

[2000SEARAY280SS]

improper torque to head settings
poor casting
warped head from over heating
improper surface preparation when replacing
over torque of blocking plugs