The old green coolant still present indicates no circulation was there after the first thermostat change I believe. Thats if you refilled the first time with other than green. Also check the thermostat you pulled out originally for a very small bleed hole.

I have found that a few times the one I removed had one or a variation of it with a closing plug for one way flow or possibly air release as I do not know everything. The chinese replacements did not but caused me no grief so far.

I always try to remain observant so if a problem of some form rears up..I can take anything unusual into consideration. I really enjoy working on cars as a pastime.

Unfortunatly even at age seventy this year I cannot seem to find enough time from other commitments. I originally told the wife when retiring at age 50. Retirement being not having to go out and earn money to sustain a decent standard of living that is. I have been so busy since then perhaps I should go back to work for the break. Originally I had mentioned to the wife if early retirement did not work out I could always go back to work.

I was always fortunate in changing out thermoststs. Usually a very simple exercise.Even here.

Then there was one of the family buggies last week. The thermostat cover neck had oxidized solid around the two studs retaining it. There was too much wiring harness etc there to use heat. So off came seven coolant hoses. The coil pack and a neck sensor I thought might be damaged from the heat.

Then I unbolted the main thermostat housing from the block. Fired up the torch and heated it up. Took three times before I could get the parts separated.

There was a little distortion to the neck flange part for my efforts. So got to level the flange as well.. This is one thermostat change that took longer than the fifteen minutes I assumed it would.

In the rust belt where we reside you do tend to run into corrosion problems of some sort fairly often. Here if you did not have ox/ac heat on hand I would not touch a car.