[Mike Noc]

Yes as mentioned these are very thermally efficient engines and if the heat isn't there to be had then using different thermostats won't help.

Why do you think they fitted fuel burning heaters? They certainly aren't cheap.

This was BMW Development's answer when the question was asked in another thread, and it tells you all you need to know:

The M47R, as we called the engine, was different to the engine for the
320D. For the Rover (75) and Land Rover (Freelander) application we used the first common rail injection system.
I went back into my documentation and have spoken to the "older" colleagues in the development about the "cold" running engine.
We have never used different Thermostat during the life span of the entire M47 engine (D and R), so we do not have different thermostats to choose from. We have introduced different thermostats for the late M57D.

Anyway, we are sure you cannot change the behaviour of the engine with a different thermostat. At the time when we introduced the direct injection diesel engine we had problems to get the engine to proper working temperature, because it was so efficient.

We remember that we had big problems to get enough heat for the passenger compartment heating, therefore we had additional heating.
Basically it would not help to get a different thermostat, because the engine will not deliver more heat and therefore the operation temperature of the thermostat does not matter.

I assume the cars are mostly driven in cities and will not get too much load on the engines. There is no other way to get the engine to hotter temperatures as to put load on them (faster driving or uphill driving!).
Sorry for this disappointing news , but if they want to play with thermostats, then I would recommend that they will take one out of the car and go to a spare part depot and have a look if they can find another one from a different car, which will fit. At that time, the supplier used mostly the same design for different car manufacturer.

BMW Group UK