I went to unscrew the radiator drain plug (drain pet****) but the head broke right off leaving the rest of it inside.

I drilled out a little bit of it so I could drain the coolant and bough a replacement plug but there are still pieces stuck inside and I cant get them out.

Should I just drill out the remaining pieces or is there a better way to get them out?

 

Uh oh. This ain't good. My (2004) did the same thing some time ago. The Hex head broke off in my 3/8 socket - but I have TWICE been able to drain the radiator, and get it to close without leaking again, by using channel locks on the 'nub' left behind.
I referred to my Factory Service Manual - cooling system and they Do Not even show a part number for the drain ****. I won't be surprised if we do not have to replace the whole radiator. I will be following your outcome. Keep us posted.







Factory Service Manual - cooling system - Pg 39

 

Someone else may be able to tell you how to get the rest out but I'd be very careful drilling. As for replacing it we'd have to know what year and engine you have. In the meantime here is a radiator petcock for a 2003 f150 5.4 liter.