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Hi All,

Long time lurker, first time poster. I recently bought a C7 Audi S6 (2012 plate) about 3 weeks ago. Car has been running ok, had a misfire which needed a coil pack changing but the other day I went to check the coolant level and found black oil in the coolant tank. Took it to a local garage to check over and they said that the ool was just sitting on top of the coolant not mixed together. They took out the oil with a syringe (we weren't able to do a coolant flush that day). The coolant underneath the oil is pink and doesn't look to have oil mixed in (I would expect a brownish/creamy sludge).

Oil in the coolant tank would indicate an oil cooler issue but in my research, the oil and coolant would be mixed together. Could it still be an oil cooler issue in this case? Anyone have any other ideas? The oil level doesn't seem to have gone down.

I've attached a pic of what it looks like now.

Thanks in advance.

If there's an issue with oil/coolant mixing, the creamy sludge tends to be in the oil (under the oil filler cap, maybe on a dipstick if you have one), not the coolant (as the oil is constantly frothed by being in the engine, whereas coolant is really only impacted by the impellers in the pump, and otherwise flows pretty cleanly.

I would expect oil to float on top of the coolant if there's a leak somewhere. Having removed the oil from the coolant so far, I'd be watching it for a bit to see if more oil appears in the coolant. You should also be watching coolant levels carefully - if you appear to be losing coolant, it will be going somewhere...