Thermostat for air-cooled VW

Chronic disease show up unexpectedly as it gets cold in air-cooled VW 1302 Super Beetle, basically the cause of dysfunction to stool of motor while idling phase is caused by the sleeping thermostat equipped on #4 cylinder playing a part of shutting the cooling air flap while it is cold, but the thermostat does not work keeping the flap fully opened leading to over cooling phenomena. Even air-cooled AD motor requires some warming up stage, the broken part of thermostat gives too much cooling air flow when the motor wants more heating for initial stage of combustion.

Though I am going to try to cheat this inconvenience by prolonging the time period of automatic choking phase.
The lack of thermostat function is clarified according to the colder climate temperature.
The colder the worse the condition becomes.
Photo shows the focus, thermostat module, fully mechanical control construction with a bi-metal function.