I'd take the stat out & fill it w water only & see if that takes care of it. The slow warmup from no stat and no corrosion resistance from no antifreeze neither of these 2 omissions will hurt you for one day. then if that's it get a stant 180 stat and good ole green antifreeze (diff opinions on AF but green stuff works for me) & button her up and adding coolant till you reach the stat housing then putting on the stat will help w air pockets

live every 24 hour block of time like it's your last day on earth