It realy depends on the crack where it is ===i have good lick with brazing with brass and silver brazing and some specialty rods for cast ===cast is difficult to repair dc over ac welders and ones that used inert gass to the weld to reduce oxidation even better==if you are not use to workimg with cast seek a prowelder who is it would be worth the fee -- when finished use a good leak suppresant in radiator along with fresh anti freeze and radiator flush == i know lot of options hope i helped

