Does anyone know what this part is on my attached picture?
It's on my alfa 159 2.0 jtdm. It's covered 63000 miles and appears to be cracked. I'm losing engine coolant out of it very slowly. I didn't realise until I was on the motorway and the car started overheating and freaking out...I filled it back up but it was almost empty again by the time I had got the 40 miles home.
It's a black box to the lower right hand side of the engine when looking from the front.
RAC man didn't seem to know what it was...any help is greatly appreciated