Re: cooled engine coolant through the upper IC ?
I would second the water / alcohol approach.
The problem with cooling down to ambient is that its really tough to get there. Heat only flows across a temperature differential, and the bigger the differential, the faster it flows. Small differential, small flow. For example, air at 50 degrees flowing across a radiator with 220 degree input water cools the water fairly effectively to something in the 180 degree range (fairly big temperature differential causing fairly significant heat transfer, and we're only looking for a 40 degree drop). However, if we take 90 degree air and try and cool 160 degree water to 100 degrees, the temperature differential that drives the heat transfer is much smaller (170 max / 130 min differential vs 70 max / 10 min differential) and will therefore require much much more surface area and air flow to accomplish.
I hope that made some amount of sense.
Either way, the "boost fluid" cooling method is probably simpler to install, and will likely yield better results. The down side is that you'll have an additional consumable, but you won't have all that plumbing (and its weight) to worry about.
'Dreamin'
