lmao import a Peugeot... I was visiting friends in Bethancourt (sp?). Yes I did see the lion briefly before taking the train back to Paris.
Higher temp t-stat means that the coolant circulating in the block etc. is allowed to reach a higher temperature before it opens and sends the coolant into the radiator, allowing the engine to reach operating temperature more quickly (or, in winter near the Alps, allowing it to reach operating temperature at all). If you have a low temp (82 degree C) thermostat and it's below freezing, you may have lukewarm coolant because the t-stat stays open allowing the rad to cool the coolant more than it should. But you know all this right?
The other option would be to block your radiator partially like long-haul truckers do in winter on their big rigs. My BJ42 has a little curtain you can pull down which I am amazed still works after 22 years. Slip some carboard or something down in there and increase the surface area covered until the desired effect is reached. That is even less work than changing the t-stat.
But does the truck underheat--I mean, what does your temp gauge say? Independent gauge? If so, does it still underheat in the summer? If it does, then you might want to change the t-stat permanently.
If the truck isn't underheating then you may have problems with your heater core.
BTW diesels as you know ignite the air-fuel by compression heating. You may get better performance if the engine is at the right operating temperature, but this is just me applying physics to the situation and I don't know if it really works out that way. I'm just a diesel disciple, after all. One of the priests should let us know.
B