Can you spot a hairline crack in the exhaust manifold?

I just have a quick question.

The turbocharger manifold on the BLS engine repeatedly leaks. Before reinstalling it, it was resurfaced to be perfectly flat. 0.6mm had to be removed. The surface of the flat area now has a noticeable sheen because it was polished, not milled.
It's possible that I made an installation error.
Original VW parts were used for the screws and seals.

But since it seems to be leaking again after being patched, I'm wondering if there's a crack visible. Nothing seemed out of place when it was assembled!

The leaks manifest as a smell when the engine is not running, which becomes increasingly stronger over time. It also becomes visible when the diesel particulate filter is regenerating. Then diesel fuel and soot leak out between the exhaust manifold and the engine.

It's difficult to say. A hairline crack often only becomes visible under stress or expansion. However, there are sprays specifically designed to reveal such cracks. Perhaps you'll get closer to the cause if it actually turns out to be a hairline crack.

Hi,

Quote:

Then diesel fuel and soot leak out between the exhaust manifold and the engine

, then it cannot be the exhaust manifold. Have you ever seen exhaust fumes coming from a diesel engine that otherwise seems to be in good condition?
hg
Herbert.

Herbert wrote:

Hi, Quote: Then diesel fuel and soot leak out between the exhaust manifold and the engine , then it cannot be the exhaust manifold. Have you ever seen exhaust fumes coming from a diesel engine that otherwise seems to be in good condition? hg Herbert

If it ignites freely, liquid will be released. Otherwise, it won't. Diesel fuel is directed to the diesel filter through the injectors, not directly into the filter. That's why it's possible for this engine to experience oil overfilling if it's driven too much on short trips.

Wrong?

vag-driver wrote:

It's difficult to say. A hairline crack often only becomes visible under stress. However, there are sprays specifically designed for this purpose. Perhaps you'll get closer to the cause if it is actually a hairline crack.

Okay, thank you, that answers my question.

Is there a specific soundscape associated with it? I once heard that there's a difference between gasoline and diesel engines.

Hi,

Quote:

If it's burning freely, liquid will come out. Otherwise, it won't. Diesel fuel is channeled through the injectors into the diesel filter.

However, with the post-injection, at worst, only a flammable mist should reach the particulate filter, not liquid. That doesn't explain the leak, though.
Try smearing the questionable exhaust manifold area and the ZK (zeta potential) at the problematic outlet with chalk, and then trigger a regeneration process. Then, just like with an oil leak on the loader housing, the leak should be visible.
hg
Herbert.

How was the manifold ground, while it was clamped in a surface grinder?

This is the alternative to milling; everything else is just a waste of time and won't produce a flat surface.

Rüdi wrote:

How was the manifold ground, clamped onto a surface grinder? This is the alternative to milling; everything else is nonsense and won't produce a flat surface

.

No idea. It was made by a workshop that had already planned to make a few exhaust manifolds for me.

Hi,

Quote:

mounted on a surface grinder? This is the alternative to milling; everything else is nonsense and won't produce a flat surface

.
Of course, there's another way to do it. I myself reworked the manifold on my old Passat using a file. One connection was almost 1 mm too short. Patiently file, repeatedly placing it on a mirror and checking it with a gauge.
Expected mileage after purchase: over 200,000 km. Connect the flange to the charger, here with the stone.
hg
Herbert.

I have no concerns about the company's work, especially since they also produce high-quality work surfaces. They do everything with machines. They even made a slide for my tailstock and the corresponding clamping tool for it, including all the necessary parts. Millimeter scale.

I'm going to disassemble the charger again, examine everything carefully, and then decide whether or not to reinstall it.

Hello!

Okay, I have to say, based on my long-term experience...
Even though that was 10 years ago:

Yes, there are cracked manifolds.
That is quite obvious.
Sometimes, you can hear turbo engines whistling.
It was definitely the case with my old T3 TD.
It made a very loud whistling noise during startup with a little bit of boost, but when the engine was warm, the noise disappeared.

And I also had the spoiled brats machined on a milling machine, as grinding wasn't possible.
That was fine as it was.

Have you ever held a ruler against the cylinder head?
Is it straight? Are the open spaces in good condition?

Are all the studs securely fastened in the head? If the exhaust manifolds warp, the resulting force can sometimes be so great that it pulls the studs out.

What material are the seals between the cylinder head and the exhaust manifold made of?

I haven't encountered problems like that before.
and I've done that many times before...

Check the entire length of the manifold with a hairline ruler.

It is also possible that the workpiece was machined and, after being unclamped, stresses were released.

You can definitely see the cracks.

Thank you for your replies!

I will report!

To be absolutely sure during assembly... the screws are normally tightened to 25 Nm. Last time, I followed that specification exactly. When I assembled this turbocharger for the first time, about 80,000 km ago, I tightened those screws to approximately 30 Nm. Everything always in several equal steps!

Since I've experienced similar leaks with another charger before, and that seal lasted for about 120,000 km, I'd rather ask this "stupid" question just in case... Because slowly, one starts to doubt oneself.

How do you always manage to tighten these types of flanges?

Or is the turbocharger overheating during the regeneration process? Could it be that a temperature sensor in the turbocharger or the diesel particulate filter is malfunctioning? Could that be related?


The seals are all original VW parts. The part between the exhaust manifold and the cylinder head is made of metal!
Which sealing manufacturer can you recommend? So far, I've only used original parts for seals on this vehicle because I've had problems with the durability of seals from other suppliers, especially rubber seals. Especially the seals on the intercooler hoses...

I have to admit, I've never used a torque wrench on exhaust manifold nuts before. This is also because, with the longitudinally mounted 5-cylinder engines, you can never reach all the nuts.

I use a 3/8-inch ratchet and tighten the bolts with a feel, working from the inside out. Whenever possible, I always replace the studs.

And I never had any problems with leaking exhaust manifolds.

Quote:

I use a 3/8 inch ratchet and tighten with a feel, from the inside out, and replace bolts whenever possible.

Same here.

I generally tighten the nuts completely, so that the seal cannot be compressed any further.

In this process, it's essential to replace all the studs and to thoroughly lubricate the threads for the nuts (e.g., with copper grease).

You would have definitely noticed cracks in the manifold due to the soot marks.

Another possible culprit is the turbo/DPF sealing ring. It's generally best to replace it. Additionally, lubricate the area around the clamp to ensure the clamp can function properly and doesn't expand unnecessarily. Furthermore, before tightening the clamp, ensure that the DPF is properly seated at its mounting points. Screw in the bolts by hand, but do not tighten them yet, so that the DPF is not under tension when the clamp is tightened.

Hmm, I probably just earned myself another negative point...

When I started disassembling the turbo, I noticed that oil or diesel was leaking along the cylinder head gasket and running down towards the timing belt side, between the exhaust manifold and the cylinder head.

The engine will be completely finished tomorrow. I still disassembled the exhaust manifold to check if it was sealed properly. The exhaust smell was probably caused by a poorly installed particulate filter. So, the manifold was sealed.
The gasket for the diesel pump/vacuum pump isn't a metal gasket, but rather a thicker paper gasket from Pierburg. Now I've installed a metal gasket again. I replaced this gasket, along with the pump, 3 months ago, which is about 10,000 km, because there were problems with the vacuum. The front of the engine was dry, while the back was wet.

The turbo itself, with its intended surface area, is perfect!

I think that after the test drive tomorrow, everything should work fine if I replace the vacuum pump seal.

Perhaps I imagined it, during the regeneration process, that he was making that noise. Perhaps the oil initially ran down into the engine due to the higher temperature during the initial burn.


The suspicion of a crack originated because a colleague had briefly looked under the engine. He then mentioned something about a crack, probably because the vacuum pump was new.