1.6 hdi sump pan/plug

I've recently bought another C3 Picasso. This one is a 2010 16v. Yesterday I changed the oil & filter (bought the car cheap with no history and SI showing minus 20k miles!).

The sump pan isn't like the ones I've seen before. They have all had the recessed plug (I'm talking 2005 Berlingo, 2011 C3 Picasso and 2012 C3 Picasso here). This one has a flush plug with a 22mm thread that uses a 10mm Allen key to loosen/tighten it.

Just to satisfy my curiosity, does anyone here know the story here? The pan doesn't look to be modified, and just to reiterate, I've had both earlier and later cars (all HDIs) with the recessed hexagon-headed plug.

TIA
Stuart.

The recessed sump plug allows around 250 ccs of oil to rest in the sump (I measured this after allowing the car to drain overnight and then removing the sump to clean the oil pickup) Some people actually just use a hammer and a drift to make them flush, It allows your new oil to look fresh a bit longer. I have seen sumps like yours on ebay, I quite like the larger drain plug too, the standard hole is a bit small and I lack patience .