So, just to confirm you have been running w/o thermostat all this while?
Thermostat is an integral part of the system, it provides back pressure to the coolant to appropriately absorb heat from the cylinder walls before travelling to the radiator for cooling, basically you are not letting the coolant do its job.
You HAVE to HAVE a thermostat.
I hope you listen to the collective wisdom of vehicle owner who have driven these for many years and know about the system well enough to provide a suggestion.
Boil the new thermostat in a pot of water to see sure that it opens and closes, i do this with non-genuine parts. i.e. pre testing.
take care and good luck.
