A cracked head or a cracked block can also cause this.
Yes, a cracked block.
you have a blown head gasket water is getting in to the engine oil
blown head gasket
blown head gasket!
If the leak is bad enough i believe it can but i would check your valve cover gasket first.
There is a strong possibility that you have either a blown head gasket or cracked cylinder head.
cracked heads or a blown head gasket can be the main source
You have a blown head gasket
blown head gasket
Possible BLOWN HEAD GASKET!!! BAD NEWS
it will cause overheating and mess up your engine internal moving parts.
Check for blown head gasket