Quote Originally Posted by Airbag79 View Post
Water has the best thermal conductivity of any liquid (~0.6 W/m K), only Mercury has a higher Thermal Conductivity (~7 W/m K). The only reason they don't allow anything but water is safety and cleanup.

Ethyl alcohol, or ethanol, is strictly for decreasing the freezing point of water. But it will also decrease the thermal conductivity of water.
The additives like Water Wetter, etc are not designed to increase thermal conductivity. They lower the surface tension of the water to improve the contact between the water and the surface that it is either absorbing heat from or dispersing heat to.