Bluish white smoke problem when cold – A6 2.5 TDI AEL

Posted: Mon May 16, 2011 6:33 pm

Hello all,

I wonder if anybody can help me shed any light on an annoying smoking problem that my A6 (2.5 TDI AEL with 197k) has developed in the last couple of months.

I’ll try and explain what happens:

When the engine is properly cold (i.e. left overnight) it will fire within a couple of seconds with a puff/small cloud of white smoke – I expect this is completely normal for this kind of age and mileage and its always been like this.

About two months ago I began to notice smoke in the mirror when pulling away from cold. It does the same if revved when stationary when its cold. I would describe the smoke as bluish-white is colour. With the car stationary revving the engine quite hard and lifting off immediately produces a cloud of smoke, but the worst situation seems to be when holding the revs at about 2000rpm which produces a huge continuous plume of smoke which blows down the road!

As soon as the engine has warmed up even a little (driven no more than a mile) the smoking seems to stop and I only get a tiny bit of grey smoke under heavy acceleration which I would think is normal.

Here is a link to a video I took which shows the smoke: Don’t stop watching too soon as the action happens in the second half! I think the guy on the moped didn’t appreciate it anyway! Laughing

http://www.thedpc.co.uk/audi.html

Has anybody else had a similar experience with this engine? Does bluish white smoke sound more like unburnt diesel or engine oil? I’ve lost about 1/4l of engine oil in about 1500 miles but, I do have a leak from the rocker cover which will account for some of that. In the same distance I’ve lost about 5mm depth of coolant from the coolant reservoir.

Things eliminated so far….

Bladerunner changed the timing belt and pump belt in January and has rechecked the timing since, so this is not to blame.

Since the smoking started Bladerunner has replaced the injectors with another cleaned up set and also checked over the fuel supply to the pump for air leaks. This had no effect on the smoking at all.

The car is as standard apart from a decat pipe as the cat was blocked.

Any help would be greatly appreciated……

Rob

Newbie Joined: Jan 20, 2009 Posts: 5

if you haven't already. Have a search on www.tdiclub.com for said smoke.

Posted: Wed May 25, 2011 11:18 pm

isn't that un burnt diesel fuel smoke?

Posted: Tue May 31, 2011 9:40 am

Nice.....

Piston rings....or turbo oil seals..?? Confused

Camped on the site Joined: Mar 04, 2008 Posts: 355

take the oil filler cap off when the engine is running, see if there is a lot of preasure trying to bolw the cap off, this could indicate rings, if not it maybe the turbo.

Posted: Wed Jun 01, 2011 12:58 pm

Thanks Jubby,

It actually does the exact opposite and tries to suck the cap down slightly.

If it is the turbo seals, can you think of any reason why the smoke would stop once the engine warms up slightly? I would have thought that it would be worse when the oil is hot?

Has anybody experienced a problem like this shortly after a decat? I've read (internet based though, so could be completely inaccurate!) that in some cases a reduction in back pressure may cause already old turbo seals to quickly give up?

Jon (BladeRunner) can you add anymore info/wisdom that may help? Smile

Thanks again.

Rob

Posted: Wed Jun 01, 2011 2:58 pm

The old oil seals on the turbo tend to contract when cool and expand when hot, so the oil could be weaping into the turbo overnight and when you start from cold it'll smoke like a good'n Shocked

.
Worth an investigation....

I have heard of smokey post decat instances, but mine wasnt particularly bad afterwards, and it was black smoke not grey / blue...

Newbie Joined: Jun 13, 2011 Posts: 1 Location: France

Hello,
I too have the same problem.
I have an A6 2.5tdi v6 afb engine.
1st thing in the morning car starts immediately, but not on all cylinders. After a few seconds bluish smoke appears from exhaust - a lot -. If I rev the engine lots of smoke billows out until its on all 6 cylinders. After that it quite normal. If I leave the car for a few hours and start it, no problem. Its only 1st thing in the morning.
I have a few suspicions:
a head gasket
fuel pump
valve stem oil seals
turbo
oil breathing component
I will do some checking this week.
Any useful info would be appreciated.
Thanks,
Dave

Bandwidth Buster Joined: Aug 12, 2006 Posts: 803

you will be best off posting about that engine in the later a6(c5) section here http://www.audifans.net/forum-6.html as our 5 cylinder versions are different,they have their own sets of problems.I am sure someone can help you on there

Posted: Fri Jul 01, 2011 4:38 pm

I had smoke after my decat, but only short-term when driven hard and it was black - just the soot of the ages being blown out.

That vid is an odd one though - as it seems that it smokes most at a particular speed (as you said) - not alot at idle - then loads - then appears to clear again at higher revs.........

What does it smell like - dieselly or burning oil? If dieselly I'm inclined to think it's an injector problem or something causing the timing to stray at particular rpm (needle lift sensor issue?). If oily then the turbo has to be prime suspect although it doesn't sound like you are using enough oil to explain this.....

Nick

Posted: Tue Jul 05, 2011 12:10 pm

Thanks everybody for your help. Bladerunner (Jon) has kindly changed one small component........the engine........and unsuprisingly this has solved the problem! Very Happy

I'll let you know what the cause was once Jon has conducted a post mortem on the old engine.

Rob

Posted: Sat Jul 09, 2011 1:47 pm

Hey all,

I am having the same problem only recently on my Volvo 850 2.5 tdi which has the same engine with 180k on it. Changed the timing belts - fuel, oil and air filters there less than 200 miles ago and since then every morning smoke has started pouring out the back, like in Rob's vid, for about 30 seconds... then its fine! Would love to find out what diagnosis Jon comes too as well on the smoking prob on your old engine Rob.

Always found you lads spoke a lot more sense re this engine than anywhere else. I have a thing for 5 pots, still owning a CQ20V too before I lumped for the swedish lump!

Needs to get out more Joined: May 03, 2011 Posts: 119

Hi,
Was there anything found ?

When I had the timing retarded, the car had difficulties starting and then produced a thick amount of "white-ish" smoke.

Now, after advancing the timing, it starts first time everytime (cold, hot, 1st day use, 2nd day use). Doesnt smoke anymore.

The only time it smokes is :

1- under hard acceleration : black
2 - if I stop the car in traffic for a long time and start moving again: whitish/grey/blue ? Not this much...
.3 - or doing what you are doing at 1300/1400 rpm. At this RPM, the engine shakes a little and produces some "white-ish" smoke but in a much lesser quantity.

The engine uses about 1 liter of oil every 4000km. I think it´s getting better now with new oil, but...

Do you have news on this ?

Posted: Sat Aug 20, 2011 8:07 pm

OT, but I'm intrigued by your username, did you used to have a Lancia?

Needs to get out more Joined: May 03, 2011 Posts: 119

OT : I actually have a red Lancia Delta HF turbo from 1988 !