Puzzling Problems with my Peugeot 406

Here, in the wild west you are required to provide the VIN number of the car you salvaged parts from when going for an inspection if you have done something major like an engine swap (or bodywork). They won't pass your car if you don't. I guess it has to do with preventing cars been stolen and broken for parts.
 
Have you solved the problem yet, Andrew?
 
Thanks for asking, WLB. I was trying to work out when was the best time to post an update, as there hasn't been a complete resolution, but neither have things 'stood still'.

The 406 had been sitting for quite some time, I'm not sure exactly how long, but the battery was not in a fully charged state. Once the battery was fully charged, all of the cooling system symptoms have seemingly disappeared.

The water in diesel fault light still is on, but not consistently. That makes me pretty sure that it is an electrical sensor/connection and not a problem with the fuel.

A new problem arose at about the same time as the cooling system faults disappeared. And this is most uncomfortable at this time of year, especially considering where I live. The air conditioning stopped working. I don't know if this was related or purely coincidental. I think that I hope the latter.

Cheers,
Andrew
 
Thanks for the comprehensive reply, Andrew.
The reason I asked is that my son's 2001 406 has a similar problem, that I was trying to figure out a couple of years ago. But he lives elsewhere now, so I've sort of forgotten about it.
When the engine is started from cold, the radiator fans run immediately, the temperature gauge needle stays in the OFF position, off-scale on the left, and the dashboard screen has the warning, Coolant level low, or something like that.
Then, after about 5 or 10 minutes of driving, and the engine has warmed up, the needle suddenly flies up to the hot end of the scale, then settles back to normal, and the low coolant warning disappears.

Cheers,
Warwick
 
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