VNT15 AFN: Common Problems and Solutions

Hi,

I have now destroyed the third turbo on the AFN.
The current one only has 15,000 km on the engine, and here's an excerpt from the seller's report:

Please provide the text you would like me to translate from German to English.
STK Turbo Technik ▪ Wiedstrasse 52 ▪ 57610 Altenkirchen

Warranty claim - No. A5768, dated July 12, 2006.
[...Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.
On July 12, 2006, we received the turbocharger mentioned here from you for processing a complaint.

1. Reference data.

1.1. Complaint Form: GAA 5768
1.2. Execution: 8900-0024
1.3. Teile- Vgl. No.: 454158-3
1.4. Serial number: 5768
1.5. Delivery note: 9158, dated August 26, 2005.
1.6. Invoice: 9158, dated August 26, 2005.

2. Conclusion.

A material or assembly defect in the turbocharger upon delivery can be definitively ruled out. Please refer to the attached inspection report for further details.

Your complaint has been rejected by us.

We are happy to answer any questions you may have.



Sincerely,
STK Turbo Technology.
Altenkirchen, July 18, 2006.


Inspection report for warranty claim - No.: A5768.

Turbocharger: 8900-0024
Serial number: 5768

The turbocharger was disassembled, measured, and inspected for any defects.
1.1. Condition of individual parts:

1 = Good, 2 = Satisfactory, 3 = Limited usability, 4 = Insufficient, 5 = Unusable.


Component | State | Comment
Tax box ________1________ OK
Compressor housing ___1________ OK
Turbine housing ____ 5________ Lubricate guide ring.
Hull assembly _______ 3 ________ OK
Compressor impeller _______ 5 ________ Impact damage.
Turbine wheel ________ 1 ________ OK
Runner wave_________5________ Bluish discoloration.
Heat shield _________ 1________ OK
Ball bearing _________ 2 ________ OK
Retaining pin _______2________ OK
Storage enclosure _______1________ OK
Axial bearings __________2________ OK
Sealing plug _____2________OK
Storage area__________2________OK
Back panel __________2________ OK

2. Diagnosis:
The runner wave is damaged. It has a bluish discoloration.
Foreign objects were sucked into the turbocharger.
The turbocharger is likely installed at an angle in the vehicle.
The turbocharger is overheating.
The O-ring is oily.
The damage was caused by faults in the area surrounding the turbocharger.
Please provide the German text you would like me to translate.


Well, great.
Since this is the third turbo that has failed, I'm seriously wondering what to do.
It probably doesn't make much sense to install a new VNT 15, as the one I have only lasts from 12 o'clock until midday. Could it be related to the installation angle of the AFN engine in the T3? Unlike in a car, the engine is installed at a 38° angle. However, the oil inlet is still at the top and the outlet is at the lowest point, as it should be.
As for the oil type, I switched to Castrol RS 10W60 during the last oil change, and the oil pressure has always been well above 1 bar. There's no further improvement possible.
The cause of the mechanical damage to the compressor is still unclear to me. I can't find any leaks or anything suspicious in the suction line or the air filter housing. The air filter is fine and is changed regularly. Could something possibly get in through the engine housing ventilation? Could too much oil mist in the ventilation system damage the compressor? By the way, the engine consumes almost no oil, maybe around 0.5 liters every 10,000 km.

What about the VNT 17? Is it more durable? What modifications need to be made during installation?

Regards,
Jens.

Hm?

The only thing that comes to mind is:

- The Ibiza 6K GP01 ASV (110 hp) has two air intakes in the underbody, of which at least one is specifically designed to cool the turbocharger with outside air - the T3 engine is not known for its tolerance of moderate temperatures. On the other hand, a small amount of outside air, or its absence, is unlikely to regularly cause a turbocharger to overheat.

- With the sentence "The turbocharger is probably installed at an angle in the vehicle," they can justify anything when you're doing a T3 conversion. However, since the 38-degree tilt axis in the T3 is parallel to the turbocharger's axis, the tilt shouldn't matter (according to my understanding of the technical aspects).

m;

Let me start by saying that you don't only hear good things about STK (to put it mildly).

What about the oil temperature? In the T3, the AFN engine doesn't get much airflow, and the oil/water heat exchanger doesn't work miracles.

Maybe you're setting it too high.

Exhaust system bottlenecks? Vacuum line leaks, or bottlenecks in the vacuum line?
Sufficient intake manifold cross-section before the turbocharger? Tuning?

In T3 vans, engine failure is often caused by overheating. An additional oil cooler might provide some relief. Have you measured or observed the oil temperature while the engine is running? Also, have you checked the temperature after the engine is turned off? I mean, even the 1.7-liter engine had thermal problems, and in most cases, these problems could only be resolved with additional cooling after being converted to a TDI engine. It's also possible that the oil pump is slightly weak (1 bar is a bit low currently; with a warm engine and around 2000 rpm, there should be a minimum of 2 bar). This could lead to insufficient lubrication, especially in the higher RPM range. The oil pressure should increase in the higher RPM range, and it should not exceed 7 bar. A discolored turbocharger shaft and a potentially cracked bearing are often symptoms of overheating or oil starvation, which usually manifests as oil leaks.


Regarding the suction issue, how was it expressed? Were the baffles damaged?

Regarding topic VNT15/GT17, the engine should normally run without any problems with the original turbocharger. The problem likely lies elsewhere and not with the turbocharger itself.

By that, I mean that even the 1.7 model had thermal problems, despite the oil cooler, .

Do you mean the 1.7-liter naturally aspirated engine?

Regarding topic VNT15/GT17, normally the engine should run without problems with the original turbocharger. The problem lies elsewhere and not with the turbocharger.

That's right, even a larger loader will eventually overheat and 'fry' under high temperatures, sooner or later.

Do you have a catalytic converter installed (it seems to be often 'forgotten' during T3 TDI conversions)?

Are you talking about the 1.7-liter engine?

Yes, or was it available as a 1.7TD? The temperature problems are common in most vehicles with a short 4-speed or a short-geared 5-speed transmission, as the engine speed is always extremely high. In addition, poor heat dissipation and heat buildup contribute to the problem.

Did you install a leak-off valve (which seems to be often 'forgotten' during T3 TDI conversions)?

That's correct. A flat and wide one would fit well behind the engine, above the transmission. Along with a 'feed pump' for the water and a well-sized oil cooler, this should help to mitigate the problems somewhat. }

Yes, or was it available as a 1.7TD?

There have reportedly been several turbo conversions done. The 1.7-liter engine is suitable for this because it already has piston cooling. However, I didn't know that it also has temperature problems even when running as a naturally aspirated engine.

Most vehicles with a short 4-speed or a short-geared 5-speed transmission experience temperature problems because the engine speed is always extremely high.

You're right - if the transmission is still the standard one, the AFN won't rev much lower.
The high exhaust gas and fresh air volume flow, as well as the high temperatures, put a significant strain on the sensitive variable geometry turbocharger (VGT) compressor.

There have reportedly been quite a few turbo conversions done. The 1.7-liter engine is suitable for this because it already has piston cooling. However, I didn't know that it already has temperature problems even as a naturally aspirated engine.

Yes, we do have cases of engine failures. Last week, we had a 1.7D engine with bearing damage. The front crankshaft journal was worn, with signs of discoloration, and the bearing shells in cylinder 1 were basically scrap. We performed all the required services and followed the oil change intervals. It looks like the lubricating film was disrupted, or there was overheating.

Jens 16syncro wrote:

. . . Turbine housing ____ 5________ Lubricate guide ring. . . .

Here's a quick question: What is the guide ring inside/on the turbine housing?
I can only imagine that it refers to the VTG adjustment ring. But how can it be lubricated (without the oil evaporating or carbonizing due to the high temperatures), if the turbocharger isn't massively ejecting oil from the bearing?

Here are a few more details:
The oil pressure of 1 bar applies at idle speed; above 2000 rpm, it is always above 2 bar, as measured at the cylinder head using a VDO auxiliary instrument.

I have an additional front oil cooler; the original water-oil heat exchanger has been removed. The oil temperature under normal operation never exceeds 95°C, as measured with a PT100 sensor in the oil pan (the PT100 sensor was calibrated to 100°C after installation).

Let it idle: Never turn it off abruptly; always let it run normally after the engine has been working hard.
Exhaust: Custom-built using V4A stainless steel pipes, of course with no bottlenecks (and no catalytic converter).
Intake manifold: It's definitely a bit "pieced together," but the narrowest diameter is located directly at the turbocharger's inlet, while the rest has a larger cross-section.

The engine is not tuned, and the only modifications made were the removal of the EGR system and the catalytic converter.
The vehicle is geared in a way that it operates just below its maximum achievable speed at its rated engine speed (4150 rpm). The maximum speed achievable with the 81 kW engine, considering factors like rolling resistance and weight, is approximately 140 km/h. I usually drive long distances at 3500 rpm, which corresponds to about 110 km/h.

And here's some more information:

I just had two pleasant phone conversations.

One with Mr. Kolberg, the CEO of STK.
His opinion on the damage pattern:
The turbocharger's mounting position is incorrect in the T3 due to the angled installation, which would prevent the oil from draining properly.
He has a point there; the oil drain hole isn't directly at the bottom, but slightly angled towards the engine block. That makes sense, because the entire engine was rotated compared to its original mounting position.
He also mentioned that a few years ago, together with Hermann Mendzigall (which brings things full circle...), he assembled a special turbocharger for the AFN engine using two housings, ensuring the correct orientation. He wants to see if he can replicate that process again. Unfortunately, Garrett no longer supplies individual parts for VTG turbochargers, which makes the whole thing considerably more difficult!
He also mentioned that the mounting position at the rear of the T3 is generally not particularly beneficial for durability. However, if I look at the cramped mounting bracket in the Golf, located between the engine block and the firewall, there isn't much airflow there either.
"Anyway, he's seen several turbos from AFN conversions installed in T3 vans before, and they all had the same overheating problems. His offers to create a custom turbo for those T3 owners were always rejected. Let's see how much he'll want for his special turbo."

I had the second conversation with Reinhold Maier:
He claims that my oil pump doesn't have enough pressure. He says it's a common mistake to leave the AFN oil pump in place and only install the suction tube from a JX oil pump. He insists that you always have to remove the entire JX oil pump. Does anyone else know about this phenomenon? I'm not sure which oil pump I have installed at the moment; I need to do some research. However, I am getting the required 2 bar of pressure, assuming the instrument is accurate (which I have never checked).

Perhaps both contribute to the premature failure of the turbocharger?

Regards,
Jens.

Sure, here is the translation of the text from German to English:

"Addendum:"
I'll post some pictures of the disassembled turbocharger here tonight.

Overall management of the AFN (Auxiliary Fuel System) in my T3 (Volkswagen Transporter).
120,000 km
First turbo replacement after 60,000 km (this was the original turbo, from VW).
Second turbocharger replacement after another 45,000 km (supplied by Turbo-Süd, Munich).
Third turbocharger after 15,000 km (supplied by STK, as they were the only ones who could supply it at the time, besides VW).
All the turbos have overheating damage and worn-out shafts. The last one was also mechanically damaged by foreign objects.

Quote:

Did you install a catalytic converter (which seems to be often "forgotten" during T3 TDI conversions)? That's correct. Behind the engine, above the transmission, a flat and wide one would fit well.

Of course, a coolant system is installed; anyone who "forgets" that doesn't understand .

"This is a Syncro, so that won't work like that. Mine is located at the rear left, between the rear wheel and the taillight, and is cooled by an air duct. An electric fan turns on at an intake air temperature of 55°C (for off-road operation). The cooling hose for the intercooler isn't great, but it's sufficient."

Regards,
Jens.

ulf wrote:

Here's a quick question: What is the guide ring inside/on the turbine housing? I can only imagine that it refers to the VTG adjustment ring. But how can it be lubricated (without the oil evaporating or carbonizing due to the high temperatures), if the turbocharger doesn't massively expel oil from the bearing?

I'll post some pictures later tonight...

Edit:
I had the images embedded in a Word file, but unfortunately, I can't extract them using a simple copy & paste . When I copy them to the clipboard and try to paste them into a graphics program, it always says "unknown format" and doesn't do anything. The file information for the images says "Image (Metafile)" with an unknown size.
Inserting it into Word or Excel works, but nothing else.
Does anyone have an idea how I can convert the images to JPG format?

Sure, here's the translation:

"Edit again:"
It's done, from Word to PDF to JPG...

Hi,

I have a customer who has a chip I installed in his AFN engine (approximately 260 Nm of maximum torque, and slightly less power due to the transmission and not particularly good cooling) in his T3. The engine had already been running for a while, and the last report was that everything was working fine.

A key issue is also the modest intercooling in this configuration.

Is the AFN standard equipment, and does the intercooler control function correctly?
Even with a hole in the air intake system, the resulting constant over-revving is unlikely to be good for the engine's lifespan.

Best regards, Rainer.

Rainer K. wrote:

A key issue is also the modest intercooling in this configuration. Is the AFN standard equipment, and does the intercooler control function correctly?

Hi Rainer,

Under normal operating conditions, the liquid cooling system provides a cooling effect of approximately 20 to 25°C below the outside temperature.
Under constant full load and low speed (e.g., a 2.6-ton vehicle pulling a 2.5-ton trailer up a long incline), the intake air temperature will definitely rise to its safety limit. A Golf with an AFN engine will certainly not perform any better in this scenario.
As mentioned before, the engine is not tuned, and the air intake is clear; I meticulously checked this before removing the turbo.

Regards,
Jens.

Edit:
Perhaps it's also due to the high stress it experiences in the van?
"My AFN engine consumes between 10 (daily driving) and 13 (towing) liters per 100 km. That's easily 100% more load on the engine compared to a small Golf! Perhaps the turbo doesn't like that. The engine itself (which has done 39,000 km in a Passat and now 120,000 km in this T3) has shown no signs of failure so far."

Okay, aside from the discolored impeller, I don't see anything unusual in the pictures. They are a bit small, but the compressor wheel looks good (or does it?), and the VTG (nozzle ring) itself also looks fine. I can't immediately see anything unusual besides the discoloration. Or am I already having vision problems?


I believe that the discoloration isn't severe, as long as it hasn't caused the wave to become distorted. There are no signs of feeding or anything similar to be seen.

Does anyone have an idea how I can convert the images to JPG?



With IrfanView, which is an image editing program (the best one I know), it's extremely user-friendly and free of charge; http://www.zdnet.de/downloads/prg/b/j/de000ABJ-wc.html.

'mullemaus' is right, it doesn't look that bad. How do you notice when a charger is about to fail, or how did a faulty charger manifest itself for you?