I got this 1996 Lexus sc400 and a week or 2 ago after a long drive from Miami Florida to Georgia it leaked all over the coolant through the overflow like that's on the resovoir, I checked for leaks filled back up and it didn't have problems no over heating so it seemed weird, until now it keeps over heating and it keeps leaking from the same place, today I changed the thermostat and still over heating

 

Air in the system?

 

I did take all the air out I put a funnel on the resovoir and let all the bubbles out for like 20 min

 

By the way when I was bleeding the system out I had the hot air on all the way and the air would only come out cold

 

Check the heater bypass valve on the firewall on the passenger side. Make sure it is opening and closing when moving the heater control from cold to full hot. If it is stuck it will prevent coolant from flowing through the heater core.
Sounds like you have air trapped in the system. Are you using Toyota red coolant?