I find that if I blow with high pressure air ( 125-150psi ) first on radiators, I can get more dirt out if dirt is dry. My blow gun has a 90degree elbow to help me get into the top of radiator on engine side. I work the dirt back and forth till radiator is clear. On fine spacing radiators air tends to blow the fine dirt out easier than packing it in with water. This is how I have been cleaning rads for a while. but if it has gotten plugged with oily dirt , then degreaser and hot water is very good. Have used my varsol gun to wash grease with varsol but hate the fumes even with great mask. What have you folks been doing to clean radiators?
compressed air for dry dusty radiators as well. water and plenty of time for after using the air to ensure its as clean as can get. oily mess with dirt, degreaser and water. steam pressure washer is good for melting the oily crud if you have access to one.
Both, air is for the day to day cleaning, eventually you will have to wash though. Dirt is an insulator and dirt on the fins will kill the cooling efficiency.