u/Business_Elevator_45

Hi everyone,

I have a PSA NFU 1.6 16V engine. About 6,000 km after a cylinder head repair, I noticed black deposits inside the coolant expansion tank.

The deposits are not oily or slippery. They are quite hard to remove and need a lot of pressure to smear. When I press on them, they smear on the plastic wall of the tank, but they do not really stick to my finger.

The coolant hoses remain soft, and the coolant does not smell like exhaust gases or fuel. There is no foaming in the expansion tank either.

The coolant was replaced during the cylinder head repair.

Any idea what could cause this?

Citroen C4 B6 2006 1.6 NFU TU5JP4