I've never heard if Evans out here, but we have Water Wetter, which appears to be a similar product. It increases the ability of your coolant to transfer heat, making the cooling system work more efficiently. Unfortunately Water Wetter costs a LOT, so I'll do other, less drastic things until I'm satisfied.

I'm trying a product from NAPA that claims to be the same stuff. When I opened the can it was clear, very thin, and smelled a little like kerosene. I'll see what that stuff does on the next warm afternoon.