2000 Beetle TDi black exhaust smoke saga

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
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I tend to drive with a light foot with my 203 TDI. I usually shift at 2,000 rpm if I am using all 5 gears. 2,500 rpm if I am using 1,3,5. I installed a performance chip which caused it to smoke a bit more than before. I then installed bigger injectors which really smoked. I adjusted the IQ so it does not smoke as much. So when I floor it, it may smoke like crazy or just smoke. I want to get a better performance chip that is aware of the injectors and have the tune set for less smoke. When I was playing with the Injection Quantity I lost horsepower when I set it to inject less and I also was not as smoky.
When I was a kid my dad would drive with a vacuum gauge trying to get as much mileage out of the big V8s we had. So when the kids got the cars they would floor it. All the deposits in the exhaust would go out during that first full throttle leaving a mighty cloud. My gas Rabbits would do the same thing as I tend to be a light foot.
So here are some of my theories. Light foot allows the oil to accumulate in the intercooler. The turbo always has a bit of oil seepage. A full throttle may move some of that through the plumbing but it is 2 feet uphill from the intercooler to the intake. You need to do a lot of high load to really blow that out. I guess if you do 110 mph hour for a half hour you might blow that clear. Another benefit of driving that fast for that long is you get the catalytic converter good and hot so it can do its job again. (Theory I read in the Internet so who knows if it is valid).
There is a test for the MAF. You hook up a Vagcom and do some third gear full throttle logging to see if the air flow meets air expected. http://www.ross-tech.com/vag-com/cars/tdi.html
I am doing a timing belt now, well if I was not on this newsgroup, my intercooler has a fair bit of oil in it. Probably as much as when I did the 100,000 mile timing belt. I might remove it to clean it out but it is just going to get oil in it again so it is probably pointless. So I am doing the 200,000 mile belt. I am not worried about the turbo. I just use Mobil 1 Truck and SUV turbo diesel oil. If you want, removing the intercooler and cleaning with some stodard solvent might humor you for a bit. There was a massive amount of oil in my intercooler at 100,000 miles. Well enough that it made a mess when I removed the out hose. But 100,000 miles later darned if there is not oil in it again. It is probably 1-2 hour task to remove and clean. It depends on if you take the bumper off to get to it or not. It is much easier to access with the bumper off.
Definition of heavy load: working hard. Driving around in third gear at 2,500 is not loaded. That is loafing. Load is driving up a 10% grade with 4 people in the car. Driving 100 mph with all the windows open is load. When I ride my bicycle at 20 mph I am often spinning at 90 rpm's. If I spin up to 100 rpm's I am going a bit faster and my load (work, wind resistance) has increased. It has nothing to do really with my rpm's. I could have changed the rear gear a tooth and I would have increased my rpm's but really not increased my load. Now as soon as I start going up a 3% grade while maintaining the same rpm's and speed my load has increased. If I make a turn and I am riding into a headwind my load has increased. What you might be doing driving 40 in third instead of 5th is increased the air volume. That might "wash" some of the oil out of the ductwork. If you really want to load it up drive hills fast, do more full throttle, drive it like you stole it. More full throttle is pumping more air through the ducts which may pump more oil out of the intercooler. Personally I just do a full throttle every now and then. If someone tailgates me I try to fog them out. Until I get a better chip I am stuck with a bit more smoke than I want.
Have you watched other TDIs take off from stop lights? I have and I have seen a small bit of particulates visible. Not a lot. Not like mine so I am not so happy with mine being dirty but I know where most of my mess is coming from. I to get ok mileage. 47-51 mpg mostly highway.
Best place for TDI propeller head stuff is over at www.tdiclub.com There may be a TDI guru where you live that may have some ideas or may be able to audit your exhaust particulates to see if it is normal.
Have you confirmed that your timing belt was changed? I think the older cars had an 80,000 mile interval. My car has a 100,000 mile interval. You can get a 100,000 mile kit installed which I think has bigger idlers or rollers. That proper timing belt kit cost $300-330 in parts and includes new idlers, tensioner, water pump and serpentine belt.
On Sat, 11 Oct 2008 12:25:38 GMT, Aawara Chowdhury

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Jim -
Thanks for the informative post. I did replace the timing belt, as well as what I would call the serpentine belt, as soon as I purchased the vehicle.
I was shifting around 1500 rpm for all 5 gears, when I was driving lightly.
I am now shifting at 2000 - 2500 rpm. It seems strange, but the vehicle seems less sluggish after I've changed my driving pattern. But less sluggish I mean that the acceleration response is better - it used to hesitate a bit (like it was struggling for air), but this doesn't happen any more.
I plan to drive at least once a week under moderate load for a long trip (say 50 miles or so). I will ask my mechanic if he can test the MAF out, but my recollection is that he doesn't have the VAGCOM software. Perhaps it is worth an investment for $250 - and I should get it myself.
AC

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I was about to put all my hoses back in but I stuck my finger in the intercooler. Seemed like a lot of oil. So I took off the front bumper and removed the intercooler. I guess I might have dumped 4 oz of oil according to the 6 oz yogurt cup I dumped the oil in. Last time I did the timing belt it seemed to have about the same amount of oil. If it was me just for fun I would get the intercooler removed and cleaned. I bet your exhaust will be a bit cleaner for a while. That bumper comes off in about 15 minutes. The intercooler comes out with 3 or 4 bolts. Well you have to get the windshield wiper reservoir out first but I had that out when I was doing the timing belt.
Some folks have the theory of drive like you stole it to keep things clean. I cannot break the frugal driving habits my father instilled 30 years ago.
Well technically you cannot do a proper timing belt change without vagcom software. You need to check timing and there is no way to accurately do it without software. It is a minor pain to finish up the timing but the only proper way. Hey, when you did your timing belt you did replace the water pump, the tensioner, the idler pulleys, and the motor mount bolts? The bolts are throw away stretch bolts and have been know to break when they are reused. The idler pulleys and tensioners are relatively cheap compared to the price of an engine if they seize.
On Sat, 11 Oct 2008 21:51:24 GMT, Aawara Chowdhury

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Hi Jim -
The idler pulleys, tensioner and mounting bolts were replaced at the same time as the timing belt. The water pump was not replaced, but it moved freely.
Over the weekend, I drove 160 miles about 70% city and 30% hwy, shifting at about 2000 rpm. Except for when I was on the highway, I never exceeded 4th gear.
This is a strikingly different way of driving than what I had been doing earlier (shifting around 1200 rpm, and rarely exceeded 1500 rpm).
We just filled the tank, and my fuel economy was 44.5 miles per gallon. This is way more than what I used to get (37 - 40 mpg), and there was little to no smoke emission (basically, a puff last night when shfting from 2 to 3, but that's all I saw).
So maybe I wasn't driving the car appropriately.
Because I am using the car at higher rpms now, I let the turbo cool down for about 30 seconds - 1 minute at idle before I shut the engine off now.
On another subject - I am thinking about using a diesel additive - I've seen a few recommendations of PowerService Diesel Kleen. What are your thoughts about this?
Thanks! AC

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I shift at 2,000 unless I am skipping gears so I might rev up to 2,500. 1,200-1,500 is probably lugging the engine.
I do not use additives. I have not seen a need for such.
Move freely is typical until they fail. Even when the seals fail they still can turn freely. Next timing belt change I would definitely change it. Many people change it as it costs less to change it out during a timing belt change than to do it as a single item. It adds 10 minutes to the task. I do not know how much they cost as I just buy the big kit which includes the pump.
On Sun, 12 Oct 2008 17:10:39 GMT, Aawara Chowdhury

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    Because TDIs have a VNT-style turbo, you need to exersize the VNT actuator mechanism on the turbo by regularly shifting at 2500-3000rpms. Not doing so regularly results in the VNT vanes getting jammed up with soot. When the vanes can't move you get an overboost situation when you do use lots of throttle and the car drops into limp mode and lights the CEL light.     Lots of low revs results in more intake clogging from the EGR system. Using more throttle also blows oil that seeped around the turbo seals through the motor so it gets consumed. The turbo oil seals need boost pressure to force them against the shaft. Babying the car results in more oil getting around those seals. A car that is babied can have a quart of oil accumulated in the intercooler.     I know it seems counter-intuitive given the excellent low-end torque of the TDI. You don't have to use full-throttle, you can accelerate modestly, but let the revs get up to 2500 or so before shifting. Freeway onramps are good for this. If you're regularly shifting at 1200 you're lugging the motor - the high torque down low masks this but it still lugging.     I shift all the time at 2500-3000 with regular runs up to 4000 or so and average 45-49mpg on my Golf TDI with the manual trans.
Todd Seattle,WA '86 GTI, Red of course. (exciting racey car) 268,000 miles '01 Golf TDI, silver. (new work car) 181,000 miles '87 Golf, Polar Silver. (retired work car) 654,000 miles <- Gone to a new home :( http://www.pureluckdesign.com <-Ferrari & VW stuff
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On Sun, 12 Oct 2008 18:15:38 -0700, snipped-for-privacy@racertodd.com wrote:

Wow to your high mileage VW. I have brought back to life a few VWs replacing or fixing about everything I could along the way. But no where near the tune of $27,000 in parts.
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