Radiator flush

I went through this with mine, sludge-o-rama. Even clogged up my first radiator. Try the Prestone radiator flush, it works ok. I personally used 2 bottles (water only no antifreeze), drove the car around for an hour, then let it sit overnight before hooking the hose up to it and letting it run for an hour. I also disconnected the lower radiator hose so the crud wouldn't get pushed into the core when running the hose.

It still discolors though, but not near as bad as in the beginning. Luckily the water in my engine gets changed regularly since I use antifreeze in the winter and straight water in the summer (to meet nhra rules).