How do you fix a radiator crack?

If its not too big and depends were its at you can use JB weld. its cheap and easy.

USUALLY,MOST CARS UNFORTUNATELY HAVE PLASTIC ENDS ON EACH SIDE OF RADIATOR ,OVER TIME THEY DECAY,A RADIATOR IS UNDER A LOT OF PRESSURE,AND THE TWO DON'T MIX,THIS COULD BE THE CASE.REPLACING THE RADIATOR IS THE ANSWER ,PATCHING IT ONLY BUYS YOU A LITTLE TIME .YOU MAYBE BROKE DOWN AGAIN SOONER THAN YOU THINK,LEAVING YOU STRANDED.NOT A GOOD IDEA TO PATCH IT.BUY A NEW ONE THAT'S CHEAPER THAN RUNNING IT HOT POSSIBLY CAUSING THE ENGINE TO OVERHEAT CRACKING A HEAD OR BLOWING A HEAD GASKET.THESE ARE VERY EXPENSIVE REPAIRS 10 TIMES WHAT A RADIATOR WOULD COST YOU.