Plastic Radiator repar?

[JMBT]

I have done the above like Rawze has shown before too. Worked great on a fresh water tank but I don't see why it wouldn't work on your Radiator. I have also have had some luck with just a butane powered hot knife. The idea with it is just to heat up the plastic and kind of smear it back and forth over the crack to seal it back up. It works well if the plastic you are working with is thick enough. Hope that helps and good luck!