Well, as far as I know, which ain't that far it goes top to top and bottom to bottom. At least thats the way all of mine have been set up and that is how I've always put them back together and none of them have burnt up yet If you run a separate cooler I've heard that you should put it in the return side of system as the in line to rad cooler would actually heat fluid up again cancelling out the effectivness of the remote cooler. I think
I'm sure that some one can explain it clearer but this is how I understand it to work.