I
suppose it's possible for a cracked head to be cracked in such a way that coolant is
leaking into chambers but not
oil but, in my experience, this is extremely rare.
Smaller Containment Dome, aka Top Hat The first containment dome failed because of ice - like crystals, called hydrates, formed at the top, clogging the pipe that was
supposed to allow the
oil to be siphoned up to the surfance, and also making the dome too buoyant to form an effective seal around the
leak.