Oooooh! This has got me going now. Decided to do a bit of reading up on antifreezes as this thread has made me realise there may be a few wee gaps in my knowledge base. So far, apart from the above discussion, I haven't found anything unexpected, except this.
Normally, when I "do" antifreeze, I mix up a 50/50 mix water/antifreeze concentrate in a 2 litre "pop" bottle, which makes it easy to get the right mix ratio and is easy to pour into the rad/expansion tank. For many years I have used distilled water (although our tap water up here in Edinburgh is very soft, no Kettle furring, so probably OK). But for a while now proper distilled water is hard to find having been replaced, it seems, by deionised water. I found Halfords selling 5 litre containers of the stuff, labeled Battery Top Up Water, at a very reasonable price so I've been using it for the last couple of years. The Punto and the Panda were both refilled with this after their cam belts/water pumps were done and the Astra was certainly topped up with it. Now I read, on a site I googled, that you shouldn't use deionised water in cooling systems because the deionised water robs ions from the metals in the engine cooling system which causes accelerated corrosion! The very thing I'm trying to avoid! (The Halfords bottle actually says suitable for topping up cooling systems though). So, not too sure about this. Should I drain and refill with a tap water or proper distilled water based solution? or am I, as usual, worrying about nothing? Opinions anyone?