A 700HP, 172mph "Cobalt" used a 33gal (264lbs) tank of cooling water in lieu of a radiator:
GM Performance Division :: Racing :: Articles :: Bonneville Salt Flats
The hassle of changing out 33gal of cooling water after each run is probably the best reason to use a radiator. Actually, I don't know that they didn't convert that water to 264lbs of steam during the run.
