As long as you let it. It will not fix itself. I'm not sure this was your complete question.
Yes
Are you talking about a crack in the engine block? Sorry, it's not repairable.
It only hurts because you've been sitting on it too long.
no
as long as it is not the winter... then it will freeze. and never put water in a hot empty radiator or you will crack the block and you will be very sorry.
yes
If the crack is weeping water (crack is next to water jacket) you could try temp fix products like chemiweld or irontite
As long as you make it take.
Marine engine blocks will crack when the water in its passages freezes and subsequently expands. If the passages are full of water inside an engine, the frozen water needs somewhere to go sotheoretically it makes room by cracking the block, hence making it bigger. If an engine was subjected to a constant 32 degrees over long enough time to freeze entirely that would be enough. However, the manufacturers install "freeze plugs" in key spots so they give before the block. This buys some time. A few cold nights wont crack a block, but winterize the engine with antifreeze before the long cold winter sets in.
It should not
Lack of anti-freeze in sub-freezing temperatures. The water in the block freezes and expands.
Antifreeze helps by not allowing the coolant to freeze and possibly crack the water passages of the block.