Loader Damage Symptoms After Rollover?

Hello,

Yesterday, I had a few issues with my car: suddenly, when I pressed the accelerator, the Polo didn't respond as usual, and I heard hissing noises.

According to the LDA, the LD value was present, but slightly lower. I immediately stopped and checked the air hoses and connectors, everything was okay. Therefore, I also suspected a leak in the LDA hose.

I then turned on the laptop and ran a few test logs with full throttle up to approximately 2500 rpm to ensure I could properly analyze the phases with the air noises.
And then it became clear: The lambda value was constantly below the target, but the air mass was above the diagnostic threshold of 1250 mg from around 1600 rpm (normally, it's about 900 mg at 1600 rpm). This essentially confirmed a leak in the charge air system, but where? As mentioned, everything looked normal.

Only during the disassembly of the upgraded SMIC did a slight oil leak at a weld seam on the intake air manifold reveal that it had cracked for approximately 10 cm. With logged boost pressures reaching 1.3 bar, several square centimeters of surface area likely blew out.
Therefore, I estimate that my charger was probably reaching speeds of up to 3200 rpm (which is when I first noticed that something wasn't right).

I then installed a standard SMIC (it's good to keep a few spare parts on hand instead of selling them), and the car is running completely normally again. The turbocharger isn't making any new noises (so far), and a wideband air-fuel ratio (AFR) log at full throttle up to 4500 rpm looks the same as it did before the problem.
The loading spool feels as usual when turned by hand: slightly stiff with a bit of play. When turning it forcefully, no grinding can be induced, meaning the gears haven't yet significantly enlarged due to the excessive speeds.

Could the charger still be faulty and fail prematurely, making it advisable to replace it before compressor debris from a potential crash causes even more expensive damage to the engine?

Or what other tests can I perform using readily available tools to get a more detailed assessment of the charger?

Hi Ulf,

Quote:

Even if the charger seems to be working now, it could still have a defect and fail prematurely, making a replacement advisable,

As long as it's not leaking oil or making any noises, just keep driving.
I wouldn't worry about over-revving with a leak. There's a guy who drives past my house every day in a 130hp PD Passat, and he goes up that hill all the time... *whoosh* *puff*

For 3 years.

I've already told the guy that he's wasting a lot of fuel with that leak (he says he's using something around 8 liters per 100km) and that the car is performing worse than necessary because I simply couldn't stand hearing that loud "PFFFFFFFFFF" sound when it starts. Unfortunately, he doesn't seem to care, and the car is still running.

Best regards, Rainer.

Rainer K. wrote:

I wouldn't worry about over-revving with a leak. There's a car that drives past my house every day, a 130HP PD Passat, that goes up the hill... sssshhhhh pfffffff Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. I've already told the guy that he's wasting a lot of fuel with that leak (he says he's using something around 8 liters per 100km) and that the car is performing worse than necessary because I simply couldn't stand hearing that loud "PFFFFFFFFFF" sound when it starts up.

Hi Rainer,

a little comfort for me
However, the noise itself does not necessarily indicate the size of a leak: a loud, sharp hissing sound usually only indicates that there is a rapid airflow somewhere, but it reveals little about the volume of air being lost.

It's possible that the Passat has only a tiny leak with sharp edges (a whistling effect), which is why it's making so much noise without the turbocharger having to work noticeably harder. And the fuel consumption... well, to understand that, you'd need to know the owner's typical driving habits.

Quote:

Perhaps the Passat only has a tiny leak

.
But not if he blows all the sand off the street with it .
I don't understand this man; isn't it that difficult to just take a look? Every day, I hear him coming from 200 meters away .

Best regards, Rainer.

Rainer K. wrote:

Quote: Perhaps the Passat only has a tiny leak . But not if he uses it to blow all the sand off the street . Every day, I can hear him coming from 200 meters away

.
Ah yes, for that, the hole needs to be "a bit bigger". If the loader can handle it for so long, it seems to have considerable reserves .
How does the Passat typically drive up a hill: with strong acceleration and high engine RPM, or more gently in a higher gear, utilizing momentum?
With higher engine load, the vehicle should also produce a significant amount of soot when going uphill, even if the engine is not receiving the correct air-fuel mixture (LD) during combustion, despite the fact that the high mass airflow (LMM) readings should be providing the full amount of air?
(When I had the LLK leak, I didn't notice any black smoke in the rearview mirror.)

Quote:

I don't understand this man; isn't it so difficult to just take a look?

It's not for us, but drivers of the type "enthusiastic user of everyday objects" would have to enter a completely different universe to understand it.

Hello Ulf,

That's not very good news.
The overloaded turbochargers I've seen all had a broken impeller shaft, and in connection with that, a defective shaft bearing.
It's important now to know for how long you over-revved the turbo. It does have some reserve capacity, after all.
I'm currently thinking about how long I can run the turbo at high RPMs without causing any damage.

The roller bearing will only break if it is subjected to excessive stress or if the bearing becomes seized.
In your case, the stress on the shaft is not particularly high, as the load was relatively low. Assuming that the lubrication of the shaft bearing was still sufficient, there is actually no reason why the shaft should break.

The only thing that could have happened is that the wave, due to its force, put more stress on the bearing, and this is now showing up as a problem.

I would keep an eye on the oil contamination in the low-pressure circuit. If there isn't a significant oil buildup here, you've probably been lucky, and the bearing is still okay.

I wouldn't switch immediately, as Rainer already mentioned.
Let's see what our engine experts have to say about this.

I'll get back to you later.
Best regards, Jochen.

Hi Ulf,

He always drives down the mountain slowly (which is good, as it's a residential area and the road is narrow), but it still always seems to emit some exhaust fumes.

Best regards, Rainer.

Jochen_145 wrote:

Now it's important to know how long you over-revved the turbo. The turbo does have some reserve.

Hello Jochen,

The total duration, encompassing approximately 10 to 15 individual operations (mostly during the logging process), is likely to be around 1 minute.

Quote:

I'm currently thinking about how long I can operate the turbo in the high-RPM range "without consequences." The loading wave will only break if there is excessive stress on it, or if the bearing becomes stuck.

Do you mean stress as a transferred (torsional) torque on the shaft?

Quote:

In your case, however, the stress on the shaft is not particularly high, as the LD was relatively low.

Yes, the "compressor efficiency" was probably not significantly overstated: it offered a higher flow rate with a lower pressure drop.
According to the pulse width modulation (PWM) signal, the turbine drive power was significantly increased: for example, approximately 70% at 1900 rpm, whereas the normal value is around 50%.
Or 48% @2500 rpm with leakage, which is abnormal (the normal value is approximately 32%, with all percentage values converted using a "100 minus logarithm" calculation).

Quote:

If I assume now that the lubrication of the bearing was still sufficient, there is actually no reason why the shaft should break.

Why might the lubrication have been insufficient? Could the lubricant film have been disrupted by excessively high surface speeds between the shaft and the bearing?
The oil was probably normally warm after about 18 km on a country road and a short stretch of highway, before I gave it full throttle for the first time.

Quote:

The only thing that could have happened is that the wave, due to its force, put more stress on the bearing, and this is now showing.

Centrifugal force... In my opinion, this would only become a problem if residual imbalances in the rotating shaft generate such high radial forces due to excessive speeds that the "egg-shaped" wave pushes the oil film away (or the oil film is already torn), leading to a kind of dry friction.

Quote:

I would keep an eye on the oil contamination in the LD circuit. If there is no significant oil buildup here, you've probably been lucky, and the bearing is still okay.

Okay, I will.

The only thing that could have happened is that the wave, due to its force, put more stress on the bearing, and this is now showing.
Centrifugal force... In my opinion, this is only likely to become a problem if residual imbalances in the rotating shaft generate such high radial forces due to excessive speeds that the 'egg-shaped' wave pushes the oil film away (or the oil film is already torn), leading to a kind of dry friction.

I would keep an eye on the oil contamination in the LD circuit. If there is no significant oil buildup here, you're probably lucky, and the bearing is still okay.
Yes, I will.

Okay, I just spoke with our engine guys.

In summary:
Based on what I was able to tell him, he believes that nothing further can happen to you. So, first of all, don't worry!

Contrary to what I initially thought, the problem with over-rotation under no-load conditions is not primarily the wave or the wave bearing, but rather the compressor blades themselves.

Fehlt der 'Gegendruck' auf der Hochdruckseite, kommt der Turbo sofort ins Pumpen, da er jetzt deutlich mehr Luftmasse abführen kann. Die angesugte Luftmasse ist jedoch durch den Querschnitt der Ansaugleitung bestimmt und kann nicht deutlich erhöht werden. Daher ist die Differenz der Luftmassen zwischen Ansaugung und Komperession zu gross. DThe turbo is pumping.
These pumps can be prone to various mechanical problems. One potential issue is that the impeller blades may shift towards the compressor housing due to the lack of counter-pressure. This inevitably leads to the destruction of the impeller blades.

However, this wouldn't have happened to you, as it would immediately occur upon pressure loss, for example, if the LL hose came loose, and it would then 'pop.'

Furthermore, diesel engines are not as susceptible to damage when a low-level hose detaches as one might initially assume.
Due to the lack of air mass in the cylinder, the exhaust volume is also smaller, which in turn means less driving energy is available to the turbocharger. Therefore, in this case, the turbocharger does not over-rev as quickly as one might think.

If the turbocharger survives the initial, significant pressure loss caused by the rupture of the low-pressure circuit, it will likely continue to function properly.

Best regards, Jochen.

Jochen_145 wrote:

If the "back pressure" is missing on the high-pressure side, the turbocharger will immediately start pumping, because it can now exhaust a significantly larger amount of air. However, the amount of air being drawn in is determined by the cross-section of the intake pipe and cannot be significantly increased. Therefore, the difference in air mass between the intake and the compression stage is too large. The turbocharger is pumping.

Hi Jochen,

"Charger pumps" exhibit high pressure buildup with low flow rates. In compressor characteristic curves, the so-called "pump line" is located on the left side: to the left of this line, the compressor essentially "free spins" because the flow separates from the impeller blades.
In the next moment, a pressure equalization occurs in reverse through the compressor because not enough fluid is flowing in the direction of the engine. When the pressure difference between the compressor inlet and outlet has decreased sufficiently, the impeller blades engage again, the turbocharger builds up new (excessive) pressure, and the process starts all over.
This type of pump cannot be referring to a leak behind the compressor, and "pumping due to insufficient back pressure" is a new concept to me... More likely, the stuffing box limit comes into play when the air being drawn in reaches (almost) the speed of sound.

Quote:

Furthermore, diesel engines are not as susceptible to issues when a low-level hose detaches as one might initially assume: Due to the lack of air mass in the cylinder, the exhaust volume is also smaller, which in turn means less driving energy for the turbo. Therefore, in this case, the turbo does not over-rev as quickly as one might think.

That sounds logical. Then the higher VTG-TV wouldn't be quite as critical as the numbers initially suggest.

Quote:

If the turbocharger survives the initial large pressure loss caused by the rupture of the coolant line, it will likely continue to function properly.

There wasn't a sudden pressure loss, because I would have definitely noticed the bang...


Thank you in any case for your research .

Hi Jochen,

'Charger pumps' exhibit high pressure buildup with low flow rates. In compressor characteristic curves, the so-called 'pump line' is located on the left side: to the left of this line, the compressor essentially 'free spins' because the flow separates from the impeller blades.
In the next moment, a pressure equalization occurs in reverse through the compressor because not enough fluid is flowing in the direction of the engine. When the pressure difference between the compressor inlet and outlet has decreased sufficiently, the impeller blades engage again, the turbocharger builds up new (excessive) pressure, and the process starts all over.
This type of pump cannot be the cause if there is a leak behind the compressor, and the term 'pumping due to insufficient back pressure' is new to me... In my opinion, the stuffing box limit is more likely to be the issue when the air being drawn in reaches (almost) the speed of sound.


My colleague also mentioned pumps in this context.
'Isn't the behavior different when the flow on the pressure side approaches infinity, while the flow on the suction side is limited? At the very least, this can also lead to the compressor blades oscillating or making a rattling noise. I'm not sure if this is also referred to as 'pumping'.'

In one of the most recent articles about pumps, Bafische wrote.

/viewtopic.php?t=13287&highlight=turbo+pumps

That is, you can reduce the compressor pump's power consumption by:

a.) reduced boost pressure.
b.) Reduce pressure before the compressor (throttling, but with a maximum potential of 50 mbar).
c.) reduce pressure loss in the charge air cooler system (including piping, etc., but with a maximum potential of 75 mbar).
d.) Optimized impeller geometry, meaning a different type of compressor.
e.) larger displacement.
f.) Two-stage charging

In the event of a leak, the pressure loss is extremely high.

Perhaps this is exactly what 'Bafische' meant, and my colleague also describes it as a 'pump.'
I'm not as knowledgeable about this as my colleague, who has experience with turbocharging TDI engines.
Therefore, I have to believe him.
For example, he was familiar with the corrosion problem of VTG (Variable Transmission Gearbox) that can occur during prolonged operation under low load conditions.

Perhaps Bafische can clarify this further.

Thank you in any case for your research.

You're welcome.

Best regards, Jochen.

Jochen_145 wrote:

Isn't the behavior different when, on the pressure side, the flow diverges towards infinity and the inflow is limited? At least, this can also lead to the oscillating or "chattering" of the compressor blades. I don't know if this is also referred to as "pumping."

The boundary conditions are completely different when the blower exhausts to the open air, namely maximum flow rate at minimum pressure build-up (pumps = minimum flow rate at maximum pressure build-up). I believe that the oscillation of the compressor blades is more likely to be caused by (supersonic) flow velocities in the extreme operating range.

Quote:

Quote: That is, you can reduce the compressor pump speed with: c.) reduce pressure loss in the charge air duct In the event of a leak, the pressure loss is extremely high. Perhaps this is exactly what Bafische meant, and my colleague also describes it as "pumps."

No, the pressure loss in the Bavarian system is caused by the flow resistance of the low-pressure pipes and the low-pressure cooler, which requires a higher pressure from the compressor than what is delivered by the motor.
If you reduce the flow resistance by using thicker pipes, etc., you can slightly lower the load on the compressor outlet (and potentially avoid the need for pumps), but the motor will still experience the same overall load as before.

Your pressure loss is something completely different: the charger is blowing air directly into the open, instead of at least feeding some of it to the engine as a "load resistance," where pressure could still build up.

Hello Ulf,

Your comment is correct. A leak on the pressure side of the turbocharger reduces the pressure ratio, and the turbocharger will then operate at its surge limit.

Since the air being drawn in reaches the speed of sound, causing flow separation on the blades, it is no longer possible to increase the mass flow rate.

However, flow separation only occurs cyclically, so the alternating presence of flow separation and attached flow leads to pressure fluctuations that manifest as vibrations and contribute to mechanical stress.

The difference between the pump line and the stuffing line is very well illustrated here:

http://www.turbodriven.com/de/turbofacts/design_compressor.asp

Best regards.

TAW

Rainer K. wrote:

Quote: Perhaps the Passat only has a tiny leak . But not if he blows all the sand off the street with it . I don't understand this man; isn't it that difficult to just take a look? Every day, I hear him coming from 200 meters away . Best regards, Rainer

So, if he's blowing sand off the road, then he's inevitably missing the lower engine cover/underbody panel, right?
At least with my 3BG model, it would never result in a "sand ingestion" situation, no matter which LL hose comes off or how large the crack in the LLK is. The bottom area is really quite well "sealed" there.
Could the exhaust system be the problem with the described 3BG, considering the whistling noise?
However, the blackening could be argued against, as it could also have other causes.
haithamina