Dude, that must hurt like a bitch. Hope it's quickly getting better . That's the kind of pain that won't let you sleep at night!
Get yourself one of these cheesy caps. They come in a few different varieties. I have one.
They are kinda gay, and sometimes they leak a drop or 2, so I have had to replace it a few times. But it could save you a bad burn.
That burn was 10+ years ago. It wasn't the cap itself. The cap AND the filler neck came off as a unit. I posted pictures of the 70K mile radiator back in '06 and it was damn near stopped up with corrosion. It still amazed me there's TRs on the road today with the original radiator.