I agree with X. Water Wetter is quite good for keeping temps down. Maybe use Distiled Water with it. No minerals or anything in the water, so no doposits will form in the plumbing. I use "Red Line Super Cool" in my Bike.
The thread i posted earlier is very good. Too bad the the images are down.
The guy did some real testing with every coolant medium he could get his hands on. the basics: water is the best, anything added to water reduces the amount of heat it can tranfer. Watter wetter makes it work better simply by lowering the suface tension of the water, which a few drops of soap will also do.
Antifreeze has a coef of 50% less than water, unless you planning on going sub-freezing don't use it.