My 1981 mercruiser 340HP 7.4L engine has water in the oil. I am trying to determine if this is due to a head gasket, a cracked head, or a cracked block. I removed all the spark plugs from and cranked the motor. Water is squirting out of the #4 spark plug hole. I doubt this is normal. Head gasket or cracked block? I sure hope it's the head gasket..