I put the new thermostat in and my car is running about 90C.
The old thermostat did not have the gasket installed properly. The gasket was just placed inside the thermostat housing and then the thermostat was pressing against the gasket.
The thermostat was not inside the center grove of the gasket.

I'm surprised that it never leaked. I think this caused the thermostat to always remain open.

Also, I snapped the head off the top bolt when removing the housing. The other 2 bolts came out easily. After 2 hours of adding pb blaster, heat, vice grips and pliers, I just installed the new thermostat and tightened the 2 good bolts. No leaks but I'd like to get the broken bolt off in the near future.

Any ideas on how to remove it without pulling the other part of the housing off the block? I'd rather not have to remove it from the block and drill the bolt out.

Pete