The thermostat case is the centrally part of cooling system.
Both cooling loops are connected in the thermostat housing.
Depending on the engine temperature the 
thermostat opens the large cooling loop (through the 
radiator).
Thermostat and 
transmitter for temperature indication are mounted in thermostat housing.
It has gland for hose connections to:
- suction pipe
 - carburettor
 - radiator
 - indermediate pipe
 - heat exchanger
 
second view:
In the exploded view Thermostat housing is number 6448.

 
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