What way is there to find out if a thermostat housing is the original bmw part? Must there be some kind of code engraved on it, or something else that will indicate its originality?

 

Why should it matter if its original? Either its working or not, correct? If its not working, replace it.

 

It matters cause it broke down after 20k km, so if it’s not a BMW original part, then I want to be careful not to buy it again.

 

Source of the busted part matters not. Replace it with the brand of your choice!

If in doubt buy OEM.

Thermostats appear to have a high failure rate, even OE is not particularly durable.

 

ΟΕΜ parts, on one hand they cost much more, they give me the feeling to last longer.
The OEM HighPressureFuel lasted 90K km and the 3rd party one (that i got for more than half the price of the OEM) lasted 50K km
So i could say that, OEM parts, have given me the feeling that they are better quality and last longer... not very much longer, but id say enough.