[supereal]

The acetic acid in vinegar takes a very long time, if ever, to reduce lime deposits in a block. The important thing is not to use anything that will attack the metal in the radiator. Years ago, we used a solution of "washing soda". I don't know if it is still available. Core sand, from the original casting, is usually hiding in he block. A coating of lime no thicker than paint, can reduce cooling efficiency by 40-50%. What is there is probably not going to move. If you use demineralized or distilled water, you won't add to the problem.