1987 Toyota Pickup antifreeze in my oil pan

Ill start by my engine was remanufactured and it was bored out 51 thousandths over and its a 4cyl 2.4 lit 22R. It started to over heat one morning on the way to work so I pulled the thermostat out and it was fine. But that wasnt the problem I figured it needed a oil change so I changed it and I found out were all my antifreeze was going no leaks outside its all internal its getting into my oil pan mixing with my oil! Please give me ideas on how to fix it or is it a loss?