Here is my take on a particular engine which overheats when the thermostat has been removed. That particular engine has another reason for overheating than whether or not it has a thermostat in place.
To answer your question about the engine taking a long time to heat up to 180 without the thermostat. That should be expected. A more significant question would be what would the temperature have been if you would not have shut it of as soon as it reached 180.
