Re. using deionized vs distilled water in cooling systems
I used to have free access to deionized water and knew from the chemists not to use it. I forgot the reasons so had to do a little research here. DI water is more conductive than distilled, thus allowing electrolytic corrosion of the cooling system metals to more easily happen.

Distilled has been exposed to the atmosphere, already absorbing CO2, while DI has not, and as DI slowly absorbs CO2 (abundant in the atmosphere) it makes a weal carbolic acid, the pH slowly going from a neutral 7 to a more acidic 5-6, thus DI has a greater tendency to galvanic corrosion as well. With the increased pressure in cooling systems this more readily happens. Although it's a closed system, there is air in the expansion tank as well as trapped air in the system.

There are different qualities of DI depending on the resin bed and time spent recirculating. In my chem lab it was on the high pure side, more so than in treated potable water systems. There appears to be a fair bit of lore about which is better to use in cooling systems among auto people. There may be more to the chemistry in auto cooling system applications than I’ve mentioned, but I do note that Prestone variously says distilled or demineralized on their website depending on where you’re reading. The main thing is avoiding heavily mineralized hard water, i.e. well water, to avoid deposits and scaling that may restrict flow.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now