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I recommend using distilled water, but I would like someone to better explain why.
When you have unlike metals in a system with fluid, they can erode. I think it's something to do with the minerals, or something in tap water, that carry electrons between unlike metals, causing them to be diodes, and electrodes, and wearing them down... Also, pure water doesn't react when super heated, like tap water does. On Mythbusters, they heated pure water beyond 212 degrees, and it didn't boil, until they dropped something into it, and it exploded into a violent boil.

Anyway would someone explain the first part?

The minerals and ions typically found in tap water can be corrosive to internal engine components, and can cause a more rapid depletion of the anti-corrosion additives found in most antifreeze formulations. Distilled or deionized water is especially important in automotive hybrid system component cooling systems, mixed with hybrid system coolant, to prevent corrosion and/or electrolysis of hybrid components. (plagiarized)

Not diode but anode cathode, electrolite. + potential difference = current flow.

When unlike metals are in contact through any aqueous solution, one material is always more Cathodic than the other...meaning it is more willing to discharge free electrons. The metal particulate in tap water becomes the Anode and makes the metal of the radiator become the Cathode. The rad deposits it's free electrons on the particles in the water.

In theory if you put a metal in the water that was more Cathodic than the rad, the reaction would be reversed and electrons would be deposited on the rad surface.

Hey i'm taking Power Engineering in college and we were taught all about pure water. So i thought i might be able to assist.

In reference to power plants, the fire-tube or water-tube boilers must have extremely pure water. Of course the water is filtered and what not to get suspended matter out, but it also has to be "demineralized" or softened. By doing this we get rid of most of the dissolved solids (magnesium and calcium) in water. Distilled water is the same thing just done by a different process.

These dissolved solids would cause "scale" to form on the boiler tubes or metal. Scale causes over-heating of the tubes and metal which in turn makes it week. So compare this to a car, if scale forms on parts the water is trying to cool, then you will get overheating. So by using distilled water you prevent the scale.

Ever find deposits of stuff in your tea kettle after using it for awhile? thats scale.

Good job, fellas!
Thanks

thanks for posting this question jesse, I'm about to fill my cooling system again and was wondering about distilled water... I guess that's what I'll use for sure!

Taylor_Matt makes another good point. Scale is very bad for the cooling process. What I was talking about is an oxidation thing. Just to clarify that these are separate, but both very serious problems.

does distilled water also not boil? for some reason i think it doesn't. mythbusters did something with distilled water not boiling. So if that is true then it shouldn't really boil, however there are minerals and s--- from your engine that would end up in there too so... thats all i have to offer haha

Everything has a boiling point. Even Titanium boils at some point. If you put nothing but water in your cooling system it would boil all right. Your engine wouldn't get to the 7-11 on the corner on a hot day. It's the Water Wetter that brings the boiling point and the specific heat way up.

http://www.youtube.com/watch?v=1_OXM4mr ... re=related" onclick="window.open(this.href);return false;

i dunno maybe im just interpreting it wrong lol

In a perfect system, the water would be pure, and would have a very high boiling point, but that wouldn't be worth the $$ it would take.

A home distiller can reduce particulate to less than 10 ppm. water is considered clean enough to drink at 500ppm...so 10ppm is very pure. Because there is almost no particulate it has very high surface tension. The fact that it is not at a rolling boil doesn't mean that it isn't hot...or that it is effectively removing heat from the engine.

The reason Glycol is used as a coolant is it's ability to shed heat. It has a higher "Specific Heat" than water. That means it takes more energy to raise the temperature of glycol and it releases heat energy easier. So even though the water doesn't appear to boil, it's specific heat hasn't changed and it is still not an efficient cooling medium.

wytbishop wrote:Everything has a boiling point. Even Titanium boils at some point. If you put nothing but water in your cooling system it would boil all right. Your engine wouldn't get to the 7-11 on the corner on a hot day. It's the Water Wetter that brings the boiling point and the specific heat way up.

thats not true at all... i've run on pure water plenty of times. didn't have time to change a leaking radiator once and jsut keep a 5 gallon jug in the back of my jeep. drove around all week no problem, doing 150+ miles a day. same with the MX... didn't have a thermostat and was going to get the system flushed soon too, so i jsut filled it with plain water in the meantime. without the thermostat, my temp gauge never even moved up to the middle. cooling properties aside, i'd always thought the main reason for coolant was its antifreezing properties

What I said is certainly true...though I may have exaggerated the point. Water is not an effective coolant.

The Ethylene in Ethylene Glycol is added to lower the freezing point. The Glycol is added to increase the cooling properties. There are other additives to reduce scale and foaming and all the other crap you don't want to happen in your engine/radiator.

'Your engine wouldn't get to the 7-11 on the corner on a hot day' is an exaggeration...? 'thats not true at all' seems an accurate response to me.

water is an effective coolant, just not *as* effective as your store bought stuff. if it wasn't, you couldn't run pure water in your car without it overheating. which you can.