I have never had any problems and yes for the most part it's particulate contamination but check the specific gravity (get a cheap anti-freeze tester) If it has broken down you will see it in the tester most important is the temp it freezes at or boils at. It gets rust in it after awhile. I have a couple friends who buy used anti-freeze from me but they do it to put in old cars that leak.

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Eat right ,Exercise ,Stay fit, Die Anyway!