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.
You have a blown head gasket
cracked heads or a blown head gasket can be the main source
There is a strong possibility that you have either a blown head gasket or cracked cylinder head.
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