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.I think my biggest concern would be the cast iron block corroding more quickly with OAT than it would with IAT. I know when I drained out the old green IAT coolant, it was 100% clean which was amazing to me. There wasn't a single flake of rust or crud that came out even though the truck has been sitting unused in a field for at least a year and probably longer. I guess when I drain this new Prestone stuff, I will see if anything comes out after being in there for a few weeks now.
That is a lot like DOT3 vs DOT5. For more than a hundred years, the old stuff worked just fine. Somebody felt the need to fix something, so they did. Is the new stuff better? Well, technically yes. But it was just fine before it was fixed. Anti-Freeze is the same way. The old green stuff did the job just fine for MORE than a hundred years. (Charles Adolph Wurtz first synthesized ethylene glycol in 1856.) Somebody just had to fix it. Is it better?