It's a nice color
Don't put it in contact with Zinc; it'll immediately displace it in whatever solid phase. If you think about how oxidation of copper proceeds:
Cu(s) --> Cu2+(aq) + 2e-
Then it makes sense that you should slow the oxidation of copper blocks with copper sulfate in solution due to Le Chatelier's principle. In terms of long term use in a cooling loop, my concern would be that you should never use it with water wetter or antifreeze (copper hydroxide will begin to precipitate above pH 5 or so). Sulfate is a tolerable electron acceptor but as long as your loop is free of sulfate reducing bacteria then I see no huge problems with microbially induced sulfides. Any idea about the wetting angle of a concentrated copper sulfate solution? That would be the only other thing that could screw cooling up I guess...