The radiator has a bleed screw on the back of it. If you release it (when cold) then you may get a hissing of air coming out.. Top up the coolant (the level will have dropped) and try running the beast again and see what happens. If you get the same symptoms and more air in the radiatore, then your gasket has been mortally wounded and needs to come off the pitch.
I wouldn't put too much emphasis on it "not overheating" - it could be that there is simply no coolant around the temperature sender, so it's just returning the temperature of the air around it. You need to bleed the system and make sure there's no air in there, then see what happens.
My guess is that there is air in the system, from a blowing gasket, and that it's pressurising the system enough to force coolant out. There's probably an airlock in the rad' but enough coolant still circulating (bottom of the rad hot, top of the rad cold) to keep the engine from overheating.. but this won't last.
Sooner or later, you'll have all air and no coolant.. then it really will overheat (though you won't see it because the sender will be reporting the air temperature, not the coolant). Warped head, scuffed pistons, melted water pump.. you get the idea.