Oops, I miss-read your first post, I thought you were flushing the water system. I'd not use CLR in an engine for flushing the coolant system. Prestone and many other companies make specific flush solutions safe for all metals and rubber in the system, why use a kitchen and bathroom cleaner to flush the system. A radiator is normally not filled with well water, it should be distilled, so there shouldn't be a build up of lime in the system.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI