Loosing antifreeze

I just drained the oil- clean just oil. After it started running hot yesterday, and I added a gal. plus, I shut it off and dip read wayyy full. I just I just did not give it time to drain out of tube. I looked under the car and saw nothing leaking. Yep I have had plenty freeze plugs leak over the years.
I pulled out thee new thermostat and ran it without and the water pump was clearing pumping well. Maybe I an get back to store and get more oil/filter and fill the rad. with water this time!!!
You put another gallon of oil in after it started to run hot?