Some temporary fixes for a leaking radiator include using cold weld epoxy, egg whites, black pepper, commercial leak repair products or duct tape if the leak is on the hoses. Using a cold weld epoxy is a reliable and safe option, however, epoxy takes up to two hours to dry.
Egg whites temporarily contain the leakage as they cook in the hot water and get pushed by the pressure into the leak. Black pepper also hardens and plugs the hole, causing the leak to subside. A commercial leak repair product can obstruct the flow of water in the radiator and should be used as a last resort.
Alternatively, weld the leak if you have the equipment and the expertise to do it yourself.