I went to Autozone and looked at a couple. Purple Power was the guys choice but it says not to use on aluminum. Simple Green is available but I never had much luck with Simple Green cleaners. These are just generic degreasers. They also have engine degreasers, with Gunk being a brand name that I recognize.
Does anyone have a particular degreaser they'd like to recommend?
You can use a pressure washer to clean your radiator, just be sure you don't have the pressure maxed out. Most pressure washers have a pressure adjustment. Have cleaned my radiator several times with a pressure washer and suffered no damage. Works best if you also have an inline water heater, which mine does...heats water up to 250 degrees....fast and efficient.