The controlling ability of the Volkswagen Thermostats is possible by the bimetal construction of the spring inside of it. This is how the thermostat on your Volkswagen knows when to open the valve and permit the hot coolant to leave the engine block and be transferred to the radiator where it will be cooled.
There are only three conditions in which the thermostat can be in when in place on your engine block. The preferred way is when it is operating normally in which it opens and closes as regulated by the heat being generated by the engine. This makes it possible for the temperature to me made constant for the best possible performance of your Volkswagen engine.
The condition that will stop your vehicle and prevent you from operating it is when the Volkswagen thermostat's valve is jammed shut. This is when no coolant is permitted to leave the engine block no matter how hot it gets. To open the valve so you can transport the Volkswagen to a repair facility, the upper radiator hose can be pulled off at the housing and a screw driver jammed down into the thermostat opening it.
The last condition is when the valve is jammed open and never closes on the thermostat. The driver will notice that the engine never reaches its optimum operating temperature when this condition is present. The passenger compartment heater will also not be capable of producing adequate heat for the comfort of the passengers as well. This is because the coolant is permitted to flow freely in and out of the engine without containment in reference to the heat being produced by the engine.