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Exhaust leak from turbo charcoal

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jsola View Drop Down
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    Posted: 24 Jun 20 at 17:06
2008 2,5TDI 174HP BPC

Hi guys I would like some opinions here. I have been having smoke leaks on my exhaust for a while. After a long search, after removing and inspecting the turbo, and refitting, I discover the leaks come from the turbo itself. There are leaks in the exhaust charcoal where it fits the CHRA, and also in the shaft of the lever actuating the variable geometry.

You can see the pictures and videos attached.
Is this normal? I have not found any reference on the web about leaks in these places!



The method I used to locate the leaks is quite basic: with the engine cold, blow fresh air into the exhaust (you can hear the air pump in the video here ) and spray soapy water in all suspected points. If in doubt, start the engine and while it is still cold confirm the bubbling and therefore the point of leakage.

The turbo runs great otherwise with lots of power and no oil leaks and noises! I even checked the axial and radial play of the turbine and found they are within specs (some 0,05mm each).


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Vanorak
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 25 Jun 20 at 23:49
Normally on a 2.5 by the time it is a big enough exhaust leak for you to smell/get choked by in the cab you will see more soot than visible in your pic and it will probably turn out to be caused by a leak on the exhaust manifold.  It is usually because of a split where the pressed steel pipes join the flange if it is an early non DPF engine like an AXD or AXE.  The later DPF equipped engines (BNZ etc) had a more robust cast iron manifold as standard and although they could crack and warp also, there were less problems.  EGR pipes and joints to the manifold can cause exhaust leaks too.

Your test looks novel Thumbs Up   I've never rebuilt a turbo myself and I wouldn't risk it because it's a specialist job to get perfect with the balancing and all.  I think there should ideally be no leakage whatsoever from where your bubbles are but it does look like a tiny leak and if your problem is the early morning asphyxiation Dead then you probably need look no further than the manifold or the EGR system.  
2004 2.5 174
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jsola Quote  Post ReplyReply Direct Link To This Post Posted: 26 Jun 20 at 11:26
Thanks for your comments T5TDI

I have checked many points in search for this leak already. Let me explain what I found so far, there are still two unrelated topics that worry me.

I found leaks on the EGR gasket. The mechanic of the seller had mounted the two EGR gaskets the other way around, had put the carton one on the hot side, and the metal one on the cold side. I had a huge leak there. I replaced these gaskets some months ago hoping that this would fix the leak.

It did not. Then I discovered another huge leak in the gasket between manifold and turbo. This leak was able to blow away a piece of paper placed nearby each time I pressed the throttle.

I also had leaks on the joint from turbo to DPF. The ring clamp was kind of loose. I hate that mechanic.

I also had oil leaks from the turbo-block joint. Yes, once that mechanic was replacing the oil gasket because of an oil leak. The rest of failures are obviously his fault.

I have been looking for leaks in the manifold itself, never found any evidence of them. Since I do not want to touch it if I can avoid it (I dont want to break the studs), I'll leave it as is until I am clear with all other causes.

So I removed the turbo last month and replaced all these joints. I also took care to inspect the turbo and concluded it was mostly OK (axial and radial plays, condition of the blades, operation of the variable geometry, .. ). 

Only when everything was assembled again I discover I still have leaks. These I located with the bubbles method. They are in two places:

1. Again, in the turbo-manifold gasket, but not in the flat metal gasket, but in the soft conical gasket that is compressed between the two triangular flanges. In this case, the upper flange is warped, and tightening the tree M12 splined bolts has the effect of making the three corners to reach metal-metal contact, thereby not allowing to fully compress the conical joint. I was about to remove the turbo again, hammer this piece flat, and refit again. 

Here is a video showing the warped flange (audio is in Catalan, but I think the video is clear enough). 

https://youtu.be/9QmyCaJZfGc

Any opinion on how to proceed?

Also, in this drawing below it seems this flange (9) should be mounted with the lips facing the other flange (facing down), but mine was mounted with the lips facing up, that is, with the flat side of the flange compressing the joint, as it seems logical. I have seen most pictures in google images where the flange is mounted like I had in the van, flat side on the gasket, and not like in this drawing. So I am inclined to ignore this drawing, even though I think it is done by VW themselves... any opinion on this?


2. But then, looking closer at the bubbles... I discovered this leak in the turbo itself, the subject of my first post. I could not find any reference of this point of leakage on the web, so I wonder if it is normal (???). I mean: there is no o-ring for the charcoal in the exhaust side, and the lever shaft for the variable geometry actuator I suspect is a tricky place to put a gasket since it is soo hot and undergoes so many extreme thermal cycles. This is why I wondered if these leaks were normal there -- I doubt it. Any opinion about this?

BTW I'll go on and put a how-to post on the turbo axle play inspection, I think it is quite interesting.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jun 20 at 10:19
I think the gasket goes with the tags facing up.  It means the gasket can grip to hang in place and not be pushed sideways when the turbo goes in.  I don't think it would matter which way up it is as long as it ends up in the correct position and undamaged.  It has been a long time since I last did that job and my memory isn't that great though!

The turbo shouldn't be leaking from the cartridge part but it would bad news to replace it and find you were still getting fumes because there was a hidden leak behind the manifold heat shield.  You could try getting under the bonnet with a torch at night and getting someone to rev the engine.  That often shows up where any smoke is blowing.  

Re the warped plate in the video - The conical ring sits slightly proud of the surface so the corners of the (thinish) steel plate will bend slightly as they tighten.  I think this is deliberate and keeps the tension on it.  It would be no good to re-use it though.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jsola Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jun 20 at 11:45
Correct, the gasket has the clips up so that it holds in position while jiggling the turbo in.

My commentary was about the "flange" or press plate (sorry I can't find a better word for it).

That is, the VW drawing has it like this (lips towards the other triangular plate pressing the conical ring):


while my van and most other places I've seen have it the other way around (lips away from the other plate pressing the conical ring):


I did replace all the gaskets (the conical ring, the triangular flat gasket, the oil gasket, and the DPF gasket!) and assembled all in with care, only to discover I had new leaks. I'm a bit frustrated with all this. I even discover I have again oil leaking, and I wonder if it was leaking from another place than the turbo gasket -- which looks perfectly dry and clean now.

Next week I take it to the mechanic see what he can do about it.

Thanks a lot for your inputs they really help!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jun 20 at 13:11
That turbo to block gasket is another one-use gasket.  On the AXE/AXD engines it is a crushable aluminium seal.  It really is strictly one-use otherwise it is almost certain to leak.  I have seen a gasket made of a different material sold online, I don't know if this is an aftermarket thing or if the later DPF vans use it as original fit.  

It is quite hard to see for certain if that turbo to block gasket is leaking unless it is pouring out because access/sight is so poor.

The torch trick is quite handy for showing up smoke.  You can also get someone to briefly put a gloved hand (because it soon gets hot!) over the exhaust to help with making any leaks puff out a bit better.  


Edited by T5 TDI - 27 Jun 20 at 21:56
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