Talltom

1994 Lexus ES 300 3.0L V6 after driving for a while the coolant will overflow out of the overflow bottle but the engine isn't overheating. I have done several things to the car with no results. Everything I read they all say head gasket and I still don't think that's what the problem is. I have done the chemical test 3 times where it shows if any o2 gases are present in the coolant and every time it stays the color blue instead of turning yellow if their where o2 gases present. I have flushed the system, new radiator cap, pressure tested the system and cant find the cause of the problem. I was just wondering if anyone has ever had this problem and what they did to resolve it, Thanks