Black coolant

[HedgeyGedgey]

What would be the possible cause of the coolant being black? Not rusty brown but really black? Cars a very tired 2005 Astra 1.6 petrol with 170k

[legless]

Sure it's coolant and not engine oil? If the head gasket is utterly, utterly fked then a complete liquid exchange might have taken place.

[HedgeyGedgey]

legless said:

Sure it's coolant and not engine oil? If the head gasket is utterly, utterly fked then a complete liquid exchange might have taken place.

Still runs fine though? Misfires in the morning sometimes. Surely it would not be happy if that had taken place?

[Romcom]

After the head gasket might be worth looking at the Oil cooler - if fitted?

[Pan Pan Pan]

Some years ago I was talking to a plumber who told me that deposits known as carbon black can build up in heating systems, and which can cause blockage, and seems to be made up of corrosion deposits amongst other compounds. When a house radiator is removed this deposit if allowe3, and to, can run out cause staining which is virtually impossible to remove.
Just wondering if it might be the same sort of thing?

[PorkInsider]

Romcom said:

After the head gasket might be worth looking at the Oil cooler - if fitted?

Oil cooler would be my guess too.

I had one go on a Golf. The coolant ended up a grey colour, rather than black, and overflowed from the header quite badly. But if it’s old engine oil I guess black’s a possibility.

On the plus side, if it is that, oil pressure is much higher than the coolant system so you shouldn’t have a lot of coolant in the oil, which could really bork it.

[LarsG]

Syphon some of the black liquid out into a glass and see if it separates. Oil will rise to the top and the water will be at the bottom.

[deltashad]

Hazarding a guess. st water with no coolant?