Peugeot 607 Temperature Gauge Fluctuations

Those symptoms point to a potential issue with the cooling system's regulation. The 'cooling grille restricted' message is a bit vague. Have you checked the relevant fuses, specifically any related to the cooling fan or any electronic components controlling the grille shutters (if your model has them)? A defective fuse can cause erratic behavior. What are the specific error codes you're seeing?

Thanks for the quick response. I'll check the fuses, that's a good shout. Where exactly would I find the fuse for the cooling fan or the grille shutters? Also, the specific error codes I was getting were P0116 (Engine Coolant Temperature Circuit Range/Performance) and P0128 (Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)). Would a fuse issue really cause those?

P0116 and P0128 confirm the coolant temperature regulation problem. Yes, a faulty fuse for the fan or grille control can absolutely trigger those codes, especially if it's causing intermittent issues. If the fuse checks out, the next step would be to inspect the coolant temperature sensor itself, and potentially the thermostat. But given the erratic behavior and the 'cooling grille' message, I'd strongly recommend getting it checked out at a workshop. It could save you a lot of time and prevent potential engine damage from overheating.

Thanks for the advice! I checked the fuses, and it turned out the fuse for the cooling fan had blown. Replaced it and the errors are gone, and the temperature is back to normal. Cost me 52€ for the new fuse and diagnostic. Appreciate the help!