That's a big leak, and it sounds like you may have gotten air in the system during the repeated refilling. If so, that's not a good thing at all (head gasket ...), and you should try to burp it out asap. If that fixes it, you need make sure something is in the tank until you can get the rad replaced. Of course it could also be a bad thermostat, but try the bleed first to see if that corrects the bouncing temps.