The cooling system is under 5-14 pounds of pressure. The cylinders are under (?) 1,000 pounds or something like that. So you are far more likely to get cylinder pressure into the cooling system than you are to get water into the oil. Often they go together, but not always ...

A12s are tough to fill as mentioned, so I suggest never change the coolant haha. It will usually burp sometime later that day or the next day and then overheat if you are not watching the temperature gauge. They don't have an effective engine bleed like some cars have.