If for example you use something like that:
mods.tconstruct.Smeltery.addMelting(liquid*100, block, 800);
for what i see the game still set as 300 (default value?)
in the modtweaker/mods/tconstruct/handlers/Smeltery.java on line #101
the variable "temp" is never used, i think the problem is on line #113 since you use
new MeltingRecipe(toStack(in), toFluid(output))
and not
new MeltingRecipe(toStack(in), toFluid(output), temp)