Every time i start the car from cold the following sequence is exact .

All climate controls set to Auto and temp set to heat.

1. Internal Fans start up and blow some air for a few seconds,
2. Dial on temperature gauge rises after a minute or two of driving,
3. The heating fans come back on distributing heat as expected
4. After around a minute of driving, the engine temp gauge drops to Zero
5. All internal bowers stop for around another minute or two before dial rises and they come back on again.

After these few minutes, all continues as normal for the most part, occasionally the needle will drop to zero again for a minute or two for what seems like no particular reason.

Any ideas welcome, I was guessing thermostat easy quick test and fix, however I hear getting at these is a bit of a pain

Worth checking both the coolant temprature sender and the oil temperature sender.

Had similar in my D3. After the initial warm up and then go cold, it ran perfectly at the right temperature for the rest of the journey
Thermostat was opening too far too quickly. Slammed a new one in and the problem went away.