Peugeot 206 Coolant Loss

I had a similar issue with my old Opel Astra diesel. Coolant level was dropping and I got a check engine light. It turned out to be a hairline crack in one of the radiator hoses. It was so small that the coolant would only leak when the engine was hot. Have you checked the hoses thoroughly while the engine is running? A pressure test could help pinpoint the leak.

That’s helpful. When you say thoroughly, what exactly do you mean? Should I be feeling around the hoses for dampness? Where were the radiator hoses placed in your Opel?

By thoroughly, I mean checking every inch of the hoses, especially near the connections and bends. Feeling for dampness is a good start. In my Astra, the problematic hose was near the engine block, almost hidden behind the air intake. Given your symptoms, visiting a workshop to do a pressure test is advisable.

I had a pressure test done and there was a tiny leak in one of the radiator hoses, just as you suspected! The mechanic replaced the hose, and the coolant level is now stable. The check engine light is gone too. The repair cost was 52€. Thank you so much for your help!