I bought a 2000 TDi beetle with 113,000 miles on it about 5 months ago. First time I've owned a diesel, but I've owned lots of gas turbo vehicles in the past.
Two months ago, I noticed that under load there was black smoke out of the exhaust. MY immediate fear was that the turbo was on its last legs, and at that point I started driving very gently - typically the engine was between 1200 - 1800 rpm. The black smoke got worse and worse.
So I took it to my mechanic cleaned the intake, and replaced the EGR valve, and the smoke went away for a week or two. At the same time, he also did an oil change, and cleaned out the tubing between the turbo and intercooler. There was some oil in this tubing, but not an excessive amount. He also could not find any boost leaks, but tightened all the connections going in and out of the turbo.
After all this, the exhaust was clean for about a week (I continued to drive very gently), but then gradually returned.
Last week I took it back to him. He floored the engine, and there was a huge amount of black smoke from the exhaust. At my suggestion, we disconnected the air mass meter, floored the engine again, and there was much less smoke.
So I drove the car for three days with the AMM disconnected. The first day there was no smoke. The second day there was a little, the third day there was more - as much as there was before I disconnected the AMM. So that seems to eliminate the AMM as the problem.
Then two days ago, while thinking about what he found the first time - small amounts of oil in the tubing between turbo and the intercooler, I had a thought.
Perhaps the turbo is leaking small amounts of oil (not unusual for a turbo of this age), and this oil remains in the tubing, unless I put the engine under load - when it gets blown to the engine, and burned resulting in the black smoke.
So I drove the car for about 15 minutes under load (3rd gear, 40 mph,
2500 rpm - 3000 rpm). The black smoke disappeared (or has greatly diminished). Now people following me only see a small amount, and that too only when I shift from 2nd into 3rd.Has anyone else noticed this? Black smoke because of oil accumulation in the tubing between the turbo and the intercooler? Is there another solution (other than replacing the turbo - which I won't do unless the situation gets much much worse). BTW, through out this my fuel economy has been between 36 - 41 mpg (all in-city driving).
Thanks! AC