I'm on my second C4 Grand Picasso, a 2.0 HDI from 2009. I've noticed that is losing coolant from... somewhere, but not showing any other obvious signs of a bigger problem. I'm having to top it up from slightly above the minimum line every 100km or so, although it's losing less with longer and faster driving - I recently went from Germany to the UK and only needed to top it up once, for example.
I don't see any obvious evidence of a leak when looking in from the top, and there's never a puddle under the car. The heating works fine, there is no smoke anywhere, and no mayonnaise under the oil cap or on the dipstick. Oddly, there's no pressure in the header tank - I opened it carefully with a hot engine and there wasn't so much of a hiss, let alone a flood of hot coolant.
I took it to my mechanic this week and he was equally confused, but after investigating with a mirror he's pretty sure that a pipe leading from the header tank to join with another pipe just under the radiator is dripping. I have traced it and found some similar-looking pipes on part websites, but I'm not sure if they are right because the part numbers seem to differ.
I've attached a couple of photos of the offending part, and I'm hoping that somebody might have already replaced one and know the part number - any advice appreciated!
