I have a 99 A6 that recently burned some kind of oil in the engine compartment. I opened the hood and looked for the origin of the smoke, it came out of somewhere between the back of the engine and the passenger compartment. If I close the hood, the smoke would be coming out from the passenger side front wheel (that's why I thought at first it was my front brake problem). Of course, if I stop at the red light, the smell will come into the passenger compartment. This went on for about a month and now the smoke stopped.

I checked my steering fluid and brake fluid, it was all fine. I changed my engine oil during this time. The only thing I am not sure is the transmission oil. If the transmission oil leaks, should I notice anything? Or this would be totally different issue? I am not sure if it was the engine burning the oil leaked onto it or if it was the converter burning it.

Anyadvice would be appreciated.

just guessing
but I had the same problem
and when I checked
cabin air filter sensor was malted
it is left from battery
goo luck

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A6 4.2 the only way to go!!!!!!!!!!!!!!!!!!

Sounds to me like your valve cover gaskets have blown. When they blow oil leakes out of the heads onto the sides of the heads and this oil burns causing the smoke that you noticed. This is a very common problem in our A6's.
Happened to me and I replaced the valve cover gaskets. Smoke and burning smell went away however I still have a leak and I know now that that is because I didn't replace the cam tensioner seals when I replaced the valve cover gaskets. So, I'll be doing the operation again in a couple of weeks. Not a hard job....takes about 4-5 hours.

thanks Golonaus and Madridlover, for sharing your experience with me. I too suspect my valve cover gasket is gone. But I don't understand is that: I started having this issue when I engine oil level was a bit low; I changed the engine oil and it still had the smoke for sometime; now without doing anything else, there is no smoke anymore. The other thing I noticed is that I used to run 8 litre per 100Km when I was at 80-90Km/h; now it is 10-20% more than before. Would this tell you anything?

Forgot to mention, when I was looking for the smoke, it was coming out from the back of the engine, and if it was from the engine body, it would be from the lower part of the engine.

Thanks.

Madridlover is correct the problem you mention is the cam tensioner seals, very common. You might want to look at the suction pump as a prentative maintance solution also. Tech articles (attached) have been written the search function would be a good place to start and don't limit yourself to audiforums there are other Audi sites that are available. Hope this helps.
Good Luck

http://forums.audiworld.com/a6/msgs/659100.phtml
http://www.audiworld.com/tech/eng67.shtml

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2003 A6 4.2 Lt Silver Ebony Trip Prem Nav Cold

Mods: K&N panel filter, winter mats, Dunlop M3 winter tires, clear corners, H-Sport sway bars

AQ6 is right about the suction pump. When I changed out my valve covers, I also changed my breather hose and suction pump. Although my old suction pump appeared to be fine it was clogging up creating the back pressure through the breather hose whitch caused the valve cover gaskets to blow. When I took my breather hose off, it snapped in two places and you could see how gungked up it was inside.
Pretty nasty.

Thanks AQ6 and Madridlover. However I still don't understand two things:

1. why it happened in the coldest days and went away on its own?
2. why the gas consumption went higher after the burning went away?

I just wanted to make sure it is impossible to be something like the transmission oil or other gear box oil that was gone. The transmission works and sounds like no problem to me.

Really appreciate the help so far. Nice articles AQ6 referred to.