For a commercially available flush, the DuPont 2-part powdered stuff is the best available. The reddish powder (cleaner) forms a weak acid that attacks lime and rust deposits, and will clean the block and the radiator core. It will also clean the rust deposits that are keeping a rotten freeze plug from springing a leak, or clean the lime deposits out of a pinhole in a radiator! The white powder is just an acid neutralizer, industrial-strength sodium bicarbonate, better known as baking soda. Follow the package dirtections, and be sure to run the neutralizer long enough to kill the acid, then do a good rinse with lots of clear water.
For the really badly clogged ones, do what I did when I was running the maintenance shop at a concrete plant- - - - -Put about 8 ounces of concentrated muriatic acid in the radiator, run it for 30 minutes at a fast idle, drain, refill, and add two boxes of baking soda and run for 10 minutes. Drain and flush thoroughly with clear water. That process will clean out anything, including cement residue! Don't ask me how it got into the cooling systems, but it was a chronic problem!
Jerry
