Ospho is phosphoric acid. It will help clean out the rust and will leave behind an iron phosphate coating. It has very littel corrosion resistance ability. Most iron phosphate coating s are used as prep before either a dry oil or paint coating. The iron phosphate crystals help adhesion for paint. If you need to clean out your engine p***ages, it can work. To prevent corrosion in future, use antifreeze. Antifreeze has corrosion inhibitors to keep the corrosion down.
I had always heard wood bleach, like you get at the hardware store, but I've never tried it. It is Oxalic acid, I believe.
Adding to what's already been said....oxalic acid use to come as a 2 part kit with sodium bicarb. Be sure to flush well and neutralize if you use an acid wash. I would pull block plugs as well to be sure. I used the 2 part kit about 20 years ago and ended up replacing the radiator and heater core a month later....don't really know if the later was a cause and effect relation though. Antifreeze corrosion inhibitors are the key thereafter
Iron***e by Kwik-Way appears to be just sodium phosphate and soda ash by the MSDS http://www.iron***e.com/PDF/MSDS%20-%20Thoro%20Flush%20(Canada).pdf This sounds like it'd be pretty gentle at least
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