i wouldn't use jb weld, i prefer epoxy. and no it's not permanent, they'll still push out if the coolant freezes. mind you nobody here runs just water for coolant....... do they? :rofl:
Not to argue, but they were never designed to push out when the water freezes. All they are there for is to seal the holes up that were used in the casting process. In all my years I have yet to see one push out and save a block.