Black substance in coolant reservoir

[Anetste]

Hi.
On our weekly engine check we noticed the coolant reservoir looked black.
When we put our finger in and scrape the sides, black stuff comes off.
Drive a mk8 custom, 2.2 TDI, euro 5 CYFF engine, 2016, 250,000km on the clock. We are in Spain.

No loss of water.
No loss of oil
No over heating
No loss of power

Any ideas of the problem or has someone else had this problem and what was the outcome. The van is booked in to the garage on Tuesday.
Thank you for reading
Annette.
I have added 2 photos but not posted with photos before.

[ned]

Looks like the oil cooler is faulty

[Anetste]

Hi. Thank you for your reply. That's a good starting point for us.

[knobby1]

Hi.
On our weekly engine check we noticed the coolant reservoir looked black.
When we put our finger in and scrape the sides, black stuff comes off.
Drive a mk8 custom, 2.2 TDI, euro 5 CYFF engine, 2016, 250,000km on the clock. We are in Spain.

No loss of water.
No loss of oil
No over heating
No loss of power

Any ideas of the problem or has someone else had this problem and what was the outcome. The van is booked in to the garage on Tuesday.
Thank you for reading
Annette.
I have added 2 photos but not posted with photos before.

Definitely your oil cooler dying...pretty common.

Lord Knobrot

[Anetste]

Thank you for your reply.
It's handy to have something to give to the garage. Hopefully the garage will know the problem but it is always handy to know before you go.