I've been checking it pretty regularly as I just wasn't convinced it was opening. The stat housing and lower hose is pretty much stone cold unless I physically restrain the fan and drive the truck hard. I don't know for sure, of course, but that pretty much has me convinced the airflow and fan alone are doing a seriously good job of cooling the head :nenau
The bottom hose is supposed to be cool...
The hot water goes into the top of the radiator, and the cooled water sinks, and goes out the bottom. On mine, often the top hose can be too hot to hold, but the bottom hose is cool, even after driving for 6 miles or so.
The radiator on the T2 is very big, and even when over half of mine was blocked with mud, it could keep the car cool, in fact, I only realised it was blocked when I stuck the caravan on the back, and she got hot going up Reigate hill.
The point of the thermostat is to stop the water from around the engine entering the radiator via the top hose before the engine is up to 82/88 degrees. Once the engine is up to that temp, the thermostat opens, letting some hot water out of the engine water jacket, into the radiator via the top hose, and pulls some cool water back in from the bottom of the radiator. This will reduce the engine temp, and the thermostat will close again. The water inside the engine is pumped around the engine and the heater matrix, regardless of whether the thermostat is open or closed, taking the whole circuit up to the same temperature.
There should never be a need on modern cars to cover the radiator, as if the engine is not getting up to temperature, it has to be either:=
the thermostat is not sealed properly, or is jammed open, or
the heater in the car is pumping out more heat than the engine can generate, or
the engine is running too weak on mixture and therefore running cool.