davidmash:
I've use JB*Weld in a hot water/high flow situation with excellent results. The only thing I'd be very careful of is being sure that the area is VERY CLEAN and I'd use a small jewlers' file to rough up the area where I'd be putting the JB*Weld on.
Remove the cap and drain just enough fluid from the neck area to provide a clean surface...then I'd clean the area up with DENATURED ALCOHOL...you should be able to get that stuff at any hardware store. Don't use rubbing alcohol...it contains oils that will screw up your repair job.
Follow the directions on the JB*Weld package and paint the stuff on in thin layers 'til it doesn't want to "flow" anymore...then you have the right consistency.
Leave it alone for 24 hours...seriously...the curing time is more important than you'd believe.
Then after all is said and done, order a new radiator and drive around carefully 'til it arrives...once that neck area starts to leak...you're going to be chasing that rabbit for a long time, or shorter if it finally breaks...which it will.
My radiator didn't break at the neck...it popped a seam on the top...couldn't stop it to save my life. Radiator and installation was about $400 ONCE they got the right one shipped (twice!!!), and about $18.00 for the anti-freeze. Some places have ... well ... let's just say the kid must have had his shoes on and pants zipped 'cause he never could count any higher than 10 when he needed to be able to handle 21...if you know what I mean...
