Can oil mixed with coolant turn black?

[KrisZ]

Today I found out the overflow coolant bottle is full of oil on my BMW motorcycle. Given how that bottle looks like, with no markings what so ever and that the actual oil fill cap is under the seat, I'm not surprised some knucklehead topped it off.

But what stumped me was how black the oil was in there. Unless the guy topped it off with used oil, I never expected it to look like this.
At first I thought it was some sort of additive in there or something.
Fortunately there was no evidence of oil in the radiator, so hopefully the system is not damaged.

Here is the mess I drained

Here is how the overflow bottle looks like, total facepalm on BMWs part.

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[cptbarkey]

Mucky, muddy brown has been my experience.

 

[Lubener]

To me, it looks like dirty oil , free of coolant.

 

[KrisZ]

To me, it looks like dirty oil , free of coolant.

Yes, it was mostly dirty oil, there was little coolant in it.

I thought about it some more and I think the previous owner may have been a victim of an attempted mechanic scam. But instead of fixing it, he decided to sell it.

He owned it for less than a year and claimed he wasn’t riding it much anymore. He had a second bike in his garage, so it was probably partially true.

 

[dumkid]

Put some water and dawn in there, run it for a few minutes, drain and refill with proper coolant. Probably just a stupid mistake

 

[JHZR2]

When I had a seeping HG there would just be a bit of black oil floating on the coolant in the bottle. Nothing else.

 

[KrisZ]

The overflow bottle was full of oil. Even though HG was my first thought, the amount was too large for it to be the case. So it either had to be added by mistake or on purpose. I lean towards it being on purpose.

I’ve been riding the bike every day a whole week without issues. The only thing that changed is it doesn’t smell like hot oil/plastic in my garage after I park it hot, which I found peculiar when I first brought it home. Now I know what caused the weird smell.