Deionized or Distilled water in a cooling system?

Coolant of choice

  • Straight Water

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86LK

Royal Smart Person
Jul 23, 2018
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I just filter my old rusty creek water through a coffee filter and put it back in. No reason to walk down to the creek if I don't have to.

50/50 is prediluted with water, no mixing needed. I believe we are talking about the concentrated versions that you have do dilute yourself.
i'm guessing you also "recycle" the coffee you drink to make more coffee, also saving that trip to the creek? :ROFLMAO:

 
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DRIVEN

Geezer
Apr 25, 2009
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*CENSORED*
I didn't even know people actually bought the 50/50 premix.
 
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86LK

Royal Smart Person
Jul 23, 2018
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I didn't even know people actually bought the 50/50 premix.
sell it all the time, even to people doing flushes who know. they just don't want to be bothered with having to go someplace else and buy distilled water. I've often wondered if the store sold $2/gal de-ionized water if "those" buyers would actually buy it and the straight coolant? not much of a price difference really
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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I will agree that softened water is probably the best if you're using water alone. But mixing soft water softened with salt wasn't recommended by some of the anti-freeze makers years ago. I remember reading that on one of the bottles at the parts store, but I can't recall which brand. DON'T USE SALT IN YOUR COOLANT!!!!!!!!!!!

I don't think there's a consensus by any of the manufacturers of either cars or coolant, and certainly not car enthusiasts, as to which water would work best. Seems like they're all over the map. In either case, (special uses excluded) water isn't normally used alone in a daily driver or weekend cruiser. That would be stupid. No corrosion protection, and the only thing you have for boiling protection is a pressurized cap that might raise the boiling point to 225 or so.

People tend to over-worry using DI or distilled water because of the valence electron imbalance due to processing to a more purer form, but at least you're minimizing the crap that's in it. You want to keep calcium and magnesium to a minimum out of your coolant system, but it's ok in your drinking water. But yeah, that purer water is going to want to suck up a bond from somewhere, and metal in your coolant system is the place it'll get it from. Again, this is only if you use pure distilled or DI water, this means it will attack the metal in your coolant system, but once it gets its fill, it's done. I still would want some anti-freeze with a corrosion inhibitor.

As for the distilled/DI issues, if you mix distilled or DI with other stuff like Prestone anti-freeze concentrate, etc., you're already adding other chemicals that are soluble in water, et al, so there's enough ions to satisfy any deficiencies in the water since now the DI or distilled is no longer a "threat" to the system as it once was. Once you add junk to water like that, you've fed it the sacrificial ions it needs. So you should be good once it is a MIXTURE. In fact, pH levels in the mixture will likely be slightly basic (around 8-ish), which is a plus. Dexcool MSDS, or now I guess they just use SDS, says it contains sodium salts, so there's your sodium ion to "fix" any DI water concerns.

Distilled water doesn't remove all volatile chemicals that could be in the water. As for "purity", DI water is likely best to use in mixing up your recommended 50/50 mixture of engine coolant but I'm not thinking a gallon or two of water that isn't constantly renewed mixed with coolant concentrate will have a ton of impurities to worry about regardless of which you choose. Sure, if you change your coolant a lot if you use straight water, or use hard tap water to top off regularly because you have a leak you can't find or fix, it will likely build up crud in the system using distilled or DI.

Assuming the data evidence found from manufacturers, you can see why this can get confusing.

Some manufacturers of the coolant use DI on their 50/50 mixes or recommend distilled water to mix to 50/50, so why can't you?

Shell's extended life 50/50 coolant mix uses DI water.
Last sentence in the gray highlighted block on the tech data sheet (ironically, the MSDS doesn't specify which type of water):

Shell coolant tech data sheet 50-50 mix water.jpeg




Prestone says you can mix with distilled water:

Prestone How To Flush and Fill.jpeg




GM doesn't seem to care as long as you can drink it and it's clean (no Camp Lejeune water).
From the 2020 GMC Sierra Owner's Manual:
2020 GMC Owner Manual Page Coolant Mix.jpeg


The 2010 and 2013 Camaro owner's manual says the same thing. 1993 Camaro Owner's manual says "clean water and proper antifreeze". The 1985 CSM for Oldsmobile Cutlass says "water and antifreeze mix".

For me, I've always used distilled or DI water to mix with coolant concentrate and "knock on wood", I've never had a coolant system failure.

I bought the 50/50 once by accident, but had no issues using it. At the time is was about 3/4 the price of the concentrate, so from a value point of view, it's more expensive than mixing your own for what you get. I prefer to mix my own with my 1 gallon graduated measuring pitcher. Not because I'm a cheap bastage, but because it's super-easy to do and I like to know for sure what's going into the system.
 
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Dayzedandkonfuzed

G-Body Guru
Feb 9, 2010
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Using Coolant - Distilled or deionized
Running straight water, with additive - Softened water
Running straight water, without additive - You do you, man.

I've seen too many vehicles (daily drivers) running straight water. When I drain it, it comes out looking like dexcool. But it's not. It's rust water. Stop it.
 
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86LK

Royal Smart Person
Jul 23, 2018
1,937
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Running straight water, without additive - You do you, man.

I've seen too many vehicles (daily drivers) running straight water. When I drain it, it comes out looking like dexcool. But it's not. It's rust water. Stop it.
those people probably got advice from the Red Green Show (after all, you ARE in Canada). he's always got great tips for automotive handymen! (y)
 
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