Super glue is not waterproof. The epoxy is, but it is not very heat resistant. I fixed the plastic top tank on a 79 volkswagon back in the 80’s with epoxy. It would hold for a few months, then start leaking again. I would just scrape it off, then redo the job. Good luck.
That’s about what I figured, so I’m thinking this is more of a temporary fix to get me through a few days. I’ll order the parts and do it right.
OK, SO to do it right you need a piece of similer plastic( there are many types actually) and you use a soldering gun or a heat gun with a focused tip .Heat the cracked area and use the repair plastic like solder. There are Pro kits for this but too much for a quiky repair. They can help ID the type of plastic your Rad tank is made of though.Ive fixed 5 or 6 with this setup and they do not leak,ever( at least where the crack was,LOL)