It's time for me to backflush the heater core that I just replaced last year. All I can figure is there was a lot of crap in the block and it is blocking flow to the core again. I pulled up the Ford service bulletin for flushing the block/core, and it calls for a cleaner to be put into the cooling system prior to flushing. I checked with my local Ford dealer, and they don't have/can't get the cleaner. They recommended I use CLR, and I know that I've read others hear have used it. I picked up some CLR, and it warns not to use it on aluminum. My question is, if I circulate this through the block per Ford's directions, is it going to give me any heater core/water pump issues due to them being aluminum?