Best Liquid Cooler fluid

You don't need to worry about corrosion unless you are running aluminium in your loop somewhere that makes contact with water. A killcoil only prevents microbial growths, it will not protect against galvanic corrosion.

Unless your loop is actually exposed to freezing temps outside, you shouldn't have anything to worry about. However, you mentioned running the rad outside, so you'll want to look into running a mixture of antifreeze or similar solution. Automotive antifreeze is fine, you would probably want to run a mixture of 30-40% or so, depending on the specs listed for mixtures of the coolant and the temps it protects against. If you are running your loop 24/7 without fail, you shouldn't have any issues with freezing, but for most people this isn't realistic.

Main sources of inadequately controlled heat are 4 HDD and the CPU. The cooling blocks for the HDD are aluminum, so I have a corrosion issue, the tubing in the radiator being copper. (I'd like to keep it that way.) The SLI'd video cards have their own externally exhausting fans.

Thanks very, for the antifreeze answer. I recall seeing warnings about using it, and Cassandras saying that it will void warranties. This goes some way toward dealing with the corrosion issue, since most good antifreeze chemistry includes anti-corrosives. (I've had good empirical scientists advise me *not* to use distilled water in automotive cooling. The reason is that the distilled water is "hungry" for metal molecules.)

The way I plan to operate the cooling is by separate power supply for pump and radiator fans. (The PSU will also be outside.) So during freezing weather I could simply run the coolant whether the computer is on or not, and turn off the radiator fans.

If anyone else shows interest, I'll post a log of my progress. As in most human enterprises, it's all an experimental process.

interesting idea. Don't know if you considered this, but make sure the radiators and hoses are in the shade outside or you'll be cooking them in the sun. Not only will you have decreased cooling performance in the summer, the UV rays will be hard on any plastic or rubber components.

Nordlead, because of the (peculiar) design of my (log) house, the radiator, fan, and PSU are all going to be directly under the shelter of an eave. Florida sun is definitely a factor. I'm considering using some tin snips to "modify" a discarded AT computer box to house the gear, since Florida wind and rain can be a problem, too.

This may sound like a paradox, but one of my reasons for this plan is to keep reservoir, pump, and radiator *below* the level of the computer rig. This will help minimize degree of disaster in event of a leak inside the computer. The room with the computer gear is above the eave, you see.

Rubix, I like EVGA components, too. Have seen several ATI cards fail for no apparent cause, even with very good cooling.

Best answer selected by davekurz.

The software has asked for judgment about best answer, but that's a tough call, since all the answers were right on and very helpful. So please don't take to any hardened heart the response about the bestest.

There are a couple premix coolants that freeze well below zero, but I can understand if you don't want to use a premix.