That doesn't make sense to me. Firstly ions are atoms already dissolved in a solution so I don't understand how water can strip ions from metal. Maybe you meant atoms, not ions. I don't know if that's true, but even if it is I don't see how tap water would not strip metal while distilled water would. Why would they behave so differently? Besides, you don't put pure distilled water in your cooling system. You mix it with good antifreeze which will prevent corrosion.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL