Some of these "old wive's tales" of fixes date back to the time before they were pressurizing cooling systems. I'm not sure some of them will work in modern pressurized radiators. I'm 74 years old and remember a couple of times when I used sodium silicate, commonly called "Water Glass," as an economical fix. I don't think the egg fix includes the yolk (I guess the "yolks on you"):-laf I think it is just the white of the egg that does the work.
That egg fix reminded me of the story my dad told about his dad and mom. Grandma saw Grandpa break an egg and put it in the radiator of the old Model T Ford. Later as they drove to town Grandma looked down and saw one of the old tires bulging and about to blow out. She yelled to Grandpa, "Bruce, Bruce, that egg is coming out of the tire!"