Super coolant won't cool down hot iron

I was experimenting with using super coolant to cool down molten iron, in order to have high thermal conductivity and not rely on slow debris-tile interactions or low TC of gasses. However, a some point, heat stop transferring, way short of the temperature equilibrium.

It might be related to clamping according to total heat difference, but the numbers don't even add up for that!

For the iron, total heat is 100 * (273 + 1444.4) * 0.449 = 77111.26kDTU

For the coolant, total heat is 10 * (273 + 132.6) * 8.440 = 34232.64kDTU