Peugeot 607 Overheating

I had a similar cooling system headache on my old Saab 9-3. Turns out, the fan relay was the culprit. The electric motor of the radiator fan only worked sporadically. It wasn't the cable itself, but the connection to the relay that was corroded. Did you check the relay for the radiator fan?

Relay... good shout. I didn't think about that. Where is it usually located in the engine compartment? And when you say 'corroded', are we talking visual gunk, or something I'd need a multimeter to diagnose?

On my Saab, it was near the fuse box, also in the engine compartment. As for corrosion, it was visible, some green crustiness on the terminals. But honestly, even if it looks clean, it's worth testing with a multimeter to be sure. But I am not an expert. If you aren't sure, maybe take it to the workshop. In my experience, fiddling with electrics can be a pain, if you don't know what you're doing.

Thanks for the advice. Took it to a shop, as you suggested. Turns out it was, indeed, a corroded plug connection right at the fan motor. They cleaned it, and all is well. Bill came to 95€ Appreciate the help!