First off, Hello to everyone! What a great site you have here!

I am trying to get my grandfathers car back on the road, It's a 94 v6 Corsica

Here are the things we have done so far.
Replaced thermostat-(old one was frozen shut)
Both coolant temps-(temp gauge would not work nor fan,did not fix fan though)
Radiator had small holes in it-(got used one from junkyard, looked fairly new)
Flushed cooling system

Here goes, yesterday we replaced the stuck thermostat an flushed the system. An we seemed to have heat finally. Well I toke it for a test drive an the check engine light came on an the temp light came on. I shut it down real quick an coasted to a pull off.. The radiator had busted where it had a small pinhole.

So today I went an pulled a fairly new radiator at a junkyard. Came home threw it in. Now seem to be back at square one. The upper hose balloon's because of so much pressure, Thought maybe the thermostat was froze an not working right, but tested it in 200 degree water an it opened up for me.. So I threw more flush in it an left the thermostat out so it could all get circulated threw.. Still would build up so much pressure that it come out the radiator cap, it even seemed to climb past half way mark on the temp gauge so I shut it down. Let out the pressure by loosening the cap. an drove it the rest way home with no problems with it overheating.But still would build so much pressure it was coming out of the cap. ( also have a new radiator cap)

Now another thing that was doing from the start, would get a puddle of water on the driver floor. I toke all the plastics off under the dash an the cover that is over the heater core. Everything was dry could not see any moisture/anti-freeze on nor around it! after driving it today when it started to over heat by the time I got home the puddle on the floor had more water there..

So does this sound like it is the heater core, an its plugged no letting coolant to circulate threw it all? I'm lost as what to do next.. Any help or suggestions would be Greatly Appreciated! Need to get my grandfather back on the road! Thanks for any help in advanced ... Oh also with the fan not working I just peeled back some plastic on the blue wire an added another wire to that straight to the positive cable so the fan would run at all times...