cleaning radiator

I have used stuff called tub and sink jelly from the hardware store. It's for removing rust and lime deposits from well, tubs and sinks. I used 2 bottles, mixed with maybe a gallon of hot water. block off the inlet/outlet, (piece of inner tube with hose clamps works good). Pour the stuff in, tilt/tip/shake the crap outta the radiator to get it through the tubes. On the 3 I have done this way, it cleaned all the crap out, and left them copper colored on the inside. Rinse well after. Good luck.