A better fan should'nt stop it at all, it's the heat causing the rise on one side(over the core that is usualy the inlet
) which lets colder water go down the other side, the colder the water in the rad the more it'll want to gravitate towards the bottom where the heat is. I don't know how well (or if) blocks with a barb at each end would work, you need the barb over core design I think, large tubing helps as well I think...
I don't know how much higher it would of gone if the alarm had'nt been set for 45DegC but it WAS under load, Safemode said he ran his for a week or so did'nt he?...