Brett
I wash my radiator about 2 times each year. I usually use simple green and I have at times uses dawn. I heat up the engine and spray the cleaner on from the inside and let it sit a while. I wash it out from the outside with the hottest water my water heater will give me after I turned it up to the hottest setting. I have a power sprayer I can turn down to a low enough setting that will not hurt the fins and that seems to work well with this hot water. I repeat this process till I see no more dirt coming out. It is really hard to see down past the fan from the inside and see those bottom corners to see if they are clean.
Ken