I have see a product called Water Wetter, that is suppose to lower the temp in the engine by 10-20°F. They have one for gassers and one for diesels. I havent heard anything bad about the stuff yet, and was thinking of trying it myself.
You can check it out here:
http://www.redlineoil.com/products_coolant.asp?productID=70
If anyone has any input on the stuff from first, second or any hand experience please advise.