I tried to address this issue in another thread i started some time ago.
http://forums.procooling.com/vbb/showthread.php?s=&threadid=3323&highlight=ambient or here's the gist of it.
Well for a little test last night, i hooked up my system with just the rad, res, and pump (I don't have a block yet.) And for those of you who thought more flow bigger pump is better, hmm.... it adds A LOT of heat to the water. Here is what I found
All temps were taken with dd5
setup is danner mag 5 rated 500gph @ 0 foot head.
4x4x6 underground electrical box for res, w/ probe mounted in it.
Black Ice Extreme w/ sunon 86cfm 120mm shrouded @ 12v.
1/2" vinyl
bout 3 quarts of tap filled system with about 1 cup anti freeze.
ambient 24c - 23c
pump left on over night without rad fan on water temp = 38c this morning.
with rad fan on 25c