There are two thermostat housings with the car when I bought it.

The reason for this is that the one that I assume was used for the car is leaking at the gasket, see the picture, so I have to start getting the other one in a better condition.

After a numbers of attempts, I have now finally found a method to polish the thermostat housing

Here is the finished result with new bolts fitted.

Temperature transmitter is used to display how hot the cooling water is on a instrument inside the car, here I have made a small YouTube video of how I have tested it.