Good idea! I've done the same thing with a retired speedometer cable. That only clears a tiny channel through the crud at the bottom of the water jacket, however. Once the drain pathway is cleared enough to flow, use a heavy dose of muriatic acid (technical grade hydrochloric) in the cooling system and run the engine until it gets up to operating temp, flush with clear water, then neutralize the acid with water and a couple of boxes of baking soda. It works much better than any of the commercial radiator flush products, and any big box hardware store will have the acid by the gallon. It's used for cleaning up after masonry jobs.
Jerry
