TDI 2.0 BRD qualmt und stinkt | Posts 16+

'Interesting theory, especially because it would explain several symptoms at once. The fact that the smell of oil and the fluctuations in idle speed only become more pronounced when the engine is warm at least supports this.'

I wouldn't be completely certain about the diagnosis until the connection can be clearly proven. Especially with the 16V TDI engines, there are several possible causes that can point in a similar direction. A crack from the glow plug hole into an oil channel would be a rather difficult fault to confirm unless the cylinder head is properly inspected.

I also find it interesting that it hasn't deteriorated much over tens of thousands of kilometers. With a normal oil leak towards the combustion chamber, one would generally expect it to become more noticeable over time.

Here's an update, as a new comment just came in: I'm now at 312,000 km, so I've already driven over 120,000 km with this problem. Nothing has changed significantly. The cracks don't necessarily have to get longer over time. However, it's very likely that they will also get wider, which would determine the amount of oil "throughput."
I recently cleaned the DPF for the first time; it was completely clogged. I had noticed that the engine felt a bit weak, but otherwise seemed to be running quite well. I had opened another topic about this because it was increasingly stalling for no apparent reason. The differential pressure sensor should have indicated this, but apparently its pressure lines are also getting clogged, so it's no longer registering properly. Now, it's running much better again; it feels like it has double the power, and I'm not kidding.
Regarding this topic: I had hoped that the reduced exhaust back pressure would also lessen the occasional odor problem inside the car, although not eliminate its cause. Unfortunately, that hasn't happened. The smell I'm experiencing inside the car likely comes from the turbocharger (otherwise, I wouldn't know where else it could be coming from). Due to the high rotational speeds, the shaft is "sealed" without physical contact, meaning it's not truly airtight, but rather, the design attempts to use the rotation of the shaft to "pump back" any leakage. And a high back pressure would have exacerbated that problem. My turbocharger isn't failing; it's probably just always been like this, but it's not very noticeable unless the exhaust smells as bad as it does now.

Why it now comes from the engine compartment into the interior remains partially unclear to me. Actually, there's a thick seal above the partition wall to the water tank. But it seems to be incorrectly designed, so that slight exhaust fumes accumulate under the hood when the car is stationary and enter the interior through this seal. Or these fumes migrate within the hood, from the engine compartment to the water tank, between the inner reinforcement and the outer shell. So, "progress through technology" .

Hello,

Do you perhaps mean "emergency mode" instead of "idle"?

"I had an issue with an unpleasant smell inside the car. It turned out that a pipe for the EGR system had a crack, which was really disgusting, especially when I was stopped at a traffic light."

The crack was barely visible, with only slight traces of soot.

Best regards, Rainer.