no, i wouldnt trust jb weld, because you know when its going to fail, when your way,way out far away from anything...lol
I weld them all the time when they come in for repair, if its a running board cooler its easy , if its the front cooler its a little more involved but still easier then changing it out. Be sure to rinse out the antifreeze in the sled/cooler, flush it out good with straight water.
If its a running board cooler, unhook the hose at each end and run water thru it. Then blow it out with compressed air from 1 end. Heat the crap out of the area with a mapp gas torch to make sure you dry up any water or the water will go straight to the heat from the tig welder and ruin the weld. ( just like soldering copper water pipe in your house, if theres water in it you cant solder it,)