There's a product called Marine Tex that's far superior to JB Weld. It's designed to survive hostile saltwater environments, and it adheres to cast iron very well. Use a small flap wheel sanding disc to smooth out the cast iron for about an inch on both sides of the crack, and don't get too obsessive about making the surface super slick- - - -a few sanding scratches help the repair bond well. Just as the repair begins to harden, press a piece of coarse sandpaper (40 grit) onto the surface of the patch to resemble the texture of the original cast iron. The patch will almost disappear, especially after it's painted. Since the 216 cooling system runs very low pressure (or none at all) a Marine Tex patch is usually leak-free. Good luck!
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