If everything is good, then something was missed. Honestly, if you are getting coolant being forced from the system and it has bubbles, it has to be the head gasket or even a cracked block or cylinder head. Do me a favor. Check engine compression. Here are links that show how to check for a bad head gasket as well as how to check for compression. You may have to do what is called a leak down test.
If we find there is one cylinder that is much different than the others, suspect the gasket. Also, let me know how the gasket was checked. In addition, how was the thermostat checked? The only way to do it is to remove it. At that point, it's crazy not to replace it.
Here is a video that shows how to confirm the gasket is good. I recommend doing it.
Let me know what you find. Please feel free to ask other questions. Based on your description, at this point, I really feel a bad gasket was missed.
Let me know. Also, let me know what you mean by the heater issues.
Saturday, January 26th, 2019 AT 5:32 PM