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I have casting sand in the lower parts & none of these methods deal with silca sand. Then I plan on running a 10:1 molasses mix through to take care of the rust, then I will remove the freeze plugs & scrape out the sand.
While engine is out and freeze plugs out scrape out the rust and sand/dirt build up first, you will be suprised at how much build up there is. A good high pressure blast inside the core area will dislodge plenty before you use the chemicals. Make sure that you at least flush out the radiator as well.