My old 98 taurus heater core was totally plugged, I disconnected the hoses to it and pulled the garden hose out there with a nozzle that butted up against the hose pretty tight. Sprayed it one way, then the other, over and over until clean water came out. Boy, that was some nasty crud that just kept flowing out of there! No heat before, but after that, it blew nice and hot. Probably not something you want your neighbors to see you doing.