In order to properly form the tubes for the radiator they will use a thin
oil based liquid with a fine sand type material. They fill the tube before they shape it into an oval to keep it from crushing flat when they run it through the roller. It also helps in keeping it from crushing flat when they cut it off to length. Just like casting sand so to speak....if it doesnt get washed out before they build the rad...it drys up and...plugged radiator brand new out of the box.