FD drainplug new position!

[birdseye]

I changed mine at 15k kms, black as ink. Changed again at 24k kms, black but not as black.
Where is all this black coming from?

In microscopic little high pressure points the already hot oil is heating up further and carbonising - in effect burning. Its also possible, depending on the rubber seals used, that its picking up some of the black from the seals. I've seen both happen and its not unusual in high load applications.

 

[RickG]

In microscopic little high pressure points the already hot oil is heating up further and carbonising - in effect burning. Its also possible, depending on the rubber seals used, that its picking up some of the black from the seals. I've seen both happen and its not unusual in high load applications.

Ain't most of the black stuff the just the surface of the heat treated steel wearing away? The gears will have been heat treated and then are often dunked in a bath of chemicals to enhance the surface properties. This turns the whole lot a black-ish colour. In time this wears away to reveal the shiney metal underneath at the points of contact - hence the oil becomes less black each time you change the oil as the coating is removed.