has anyone had their engine replaced due to bad castings allowing air to get in

This problem happens OFTEN...but bad castings are NOT the problem! What really happened is it got too hot and blew the head gasket and/or cracked the head (only slightly enough that it isn't noticable) and after "repairing the water pump" the problem suddenly appears. You CANNOT get all of the air out of the system because the engine is continuously pumping air into the cooling system through the blown gasket or crack in the head! Think about it! . . . And suppose you DID have a bad casting? What do you think will happen when you drive it? The cooling system would get hot and build up pressure and guess what? IT WILL LEAK OUT! It won't suck in air!

never heard of that in my life.seek a 2nd opinion