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Old 02-20-2006, 03:04 PM
bioTD bioTD is offline
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Join Date: Apr 2005
Location: Portland, OR
Posts: 11
The main difference between de-ionized and distilled is the way it is produced. One by evaporating and recondensing, the other by chemical purification process. The actual chemistry depends on the method and equipment used. For the purpose of mixing with coolant, either is fine. If you have free supply of de-ionized use it. There are actually ASTM specs for water to mix in regents, I think ASTM D1193 Specification for Reagent Grade Water.

For the purpose of putting into your engine, deionized or distilled is agressive against metal (especially cast iron block), but if run in a circle in your cooling system it would come to equilibrium and will definitely be fine once mixed with coolant. Tap water has dissolved solids and things that precipiate and build up in you block and radiator, that's why recommend to not use tap water.

I also work at a place with free DI water and have been using it for years. You can even use unmixed to 'flush' the crud out of your cooling system, since it will try to pick up the deposits that are already in there.
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