The theory behind running a thermostat housing rather than
running with no thermostat, is that you need to provide some
restriction in the system to slow the coolant flow.
If you run with no thermostat, the coolant circulates to
quickly. The coolant will pick up the heat in the engine but
then can not get rid of it because it does not spend enough
time in the radiator. So it circulates back into the engine
still hot with very little heat capacity left. So the net
result is that you can actually run hotter without a
thermostat than with one.
The restriction allows the coolant to spend more time in the
radiator and get cooled off before returning to inferno in
the engine block.