Is it leaking? Drive it, then throw a piece of cardboard under it. If no leaks, try the synthetic route. Use 5-40, 5-50, or if cold start isn't a problem, try 15-40 or 15-50. Molecules of synthetic are supposed to be more nearly the same size, not an average, so the smaller molecules of regular oil don't escape. Worked for me ( on three engines, all diesel).

We have solved problems like this by replacing clogged breather boxes (oil and vapor seperator) under the intake manifold. Of course I assume that all of the PCV system including the actual ports into the intake manifold are clear.

Smoke coming out the tailpipe when the engine is first started indicates oil is leaking internally. One likely culprit would be the valve seals. Another could be the turbo.

Still, a quart every two or three weeks is high unless you are putting on a lot of miles. It would not be unusual for a high milage car to use 2 quarts in 3,000 miles.

How often did you change the oil in the first 120,000 miles?

First question is--how many miles do you put on in the "two to three weeks"?

Going to synthetic may reduce visible smoking (but leave consumption the same).
On the other hand, if you are running hot, synthetic is more stable and less likely to evaporate when hot.

You might consider doing a service with a product called AutoRX. Have seen some very good reports on it, though haven't had a need to use it myself.
It apparently will clean and soften seals over a couple thousand miles.
At worst, you'll be out $25 or so, and it could help.

I think the time to have switched to the synthetic was about 120,000 miles ago. Synthetic won't reduce oil consumption and may increase it at this point. I agree with the other poster, switch to a heavier weight oil (see the chart in your owner's manual) until it gets worse or the source becomes apparent.

BTW, DO check the oil level with the car on a dead level surface when the car is cold and if your car has an oil cooler the fill capacity is about 6.5 quarts, not 6.

-Punx

Synthetic oil is not going to reduce the consumption. Either the engine is burning it or leaking it.

You might slow the loss down by going to a step thicker grade of oil. 15W-40 is a good summer grade oil for these engines (my '96 recommends it for all except the coldest weather).

Most places seem to put 5W-30 or 10W-30 oil in as a matter of course.

Other than that, crystal ball diagnosis is pretty hard!

John