Engine temperature - 850 TDI

My engine temperature sometimes changes (getting colder) a little e.q. when
driving down-hill or when
idling in traffic jams.

Is this normal or a sympton on a defect thermostat?

Regards Per

 

Not an expert, but I think it's normal, at least in winter. The engine is
producing less heat when the throttle is lifted, and diesels breath the same
amount of air per revolution regardless of whether it is light throttle or
full throttle (short of the turbo spinning up).

Mike