VTG Loader Wear: Prevent Damage After Startup

Hello,

Sometimes I still remember my first turbocharged engine (1.4L gasoline) from the 80s, which had a red warning label that reminded the driver not to accelerate too forcefully immediately after starting the engine, because the turbocharger could be damaged due to a lack of oil pressure.

Back then, mineral oil with a viscosity of 15W-40 was the standard, but the fundamental problem of oil starvation after a prolonged period of engine operation can still be heard in many TDIs today, even those that run on 5W oils: a loud, rattling sound from the valves for a few seconds, until the oil pressure reaches the cylinder head and the hydraulic lifters are filled.
Our ALH Ibiza (without the engine cover) puts on quite a show every morning...

Whenever I think about the oil supply to our VTG loaders in these situations, considering that the oil is delivered through a thin oil pressure pipe with an estimated internal diameter of 3 mm and a length of 1.5 meters, I have a gut feeling that a stable oil supply to the loader will only be guaranteed when the hydraulic pumps stop making noise.

Am I unfairly criticizing things here, simply because modern designs, thanks to clever lead-in geometries, capillary action, etc., ensure that after an initial lubrication (after the initial installation or replacement), a continuous column of oil remains from the pump to the roller bearing supports of the charging pump? This column of oil never breaks, even after the engine is turned off and has been properly run with the thinnest oil?
Then, the initial oil pump priming would already start the oil flow through the supercharger when the engine is idling, so that you could actually engage the clutch and accelerate immediately upon starting the engine, without risking damage to the supercharger due to oil starvation.
However, as soon as this theoretical oil column is interrupted anywhere between the pump and the turbocharger when the engine is not running – and I assume it is – the turbocharger will not receive oil pressure for certain periods after each engine start, and these moments are extremely critical, as any TDI driver with even a basic interest knows.

Nevertheless, thanks to the standard turbocharger control software, the VTG immediately closes upon starting: this converts the combustion of the excessively rich starting mixture, which instantly accelerates the engine to approximately 1100 rpm, into a much more powerful drive for the turbine wheel than would be possible with a wastegate turbocharger, as was installed in the car with the aforementioned turbocharger warning label.

Depending on how long it takes for the turbocharger to start producing a steady, clean oil flow after initial spool-up, an impatient driver might, without realizing it, perform a forceful start with high engine load and corresponding turbocharger boost, before the turbocharger's lubrication is properly established.
However, when the oil pump actually starts providing stable oil pressure after the engine is started, and what might happen before that, seems to be a topic that is no longer widely discussed these days.
Because technically motivated warning signs no longer fit into the world of generally suggested technical perfection, and might be portrayed as a sign of backwardness in comments from "expert" media?
Or perhaps because premature turbocharger failures are so rare in TDIs that one doesn't apparently need to consider developing one's own countermeasures?

I would love to see a statistic that correlates the achieved mileage of VTG-TDI turbochargers until failure with the user's driving profile immediately after engine starts. I'm willing to bet that drivers who frequently accelerate rapidly from a standstill will, on average, have to replace their turbochargers sooner than drivers who buckle up and wait a bit before driving off after starting the engine.
However, since such statistics are, to my knowledge, not kept anywhere, this topic remains speculative.

The fact is that, at least in the EDC15 software, there is a timer that allows the VTG (Variable Turbine Geometry) to remain open for a selectable period of time after each engine start, depending on the coolant temperature, even if the driver immediately floors the accelerator: as long as the timer is running, the engine only pulls like an SDI (direct injection) engine.
This software concept clearly demonstrates that the developers were well aware of the engine starting problem – but what does VAG do with this information?
In all the data points I have examined, this timer is consistently set to zero, although, in my opinion, every second of "VTG open" after the engine start would extend the expected lifespan of the charger.


OK, I can already guess Bertil's response: Today's emission measurement cycles no longer include a warm-up period for the engine after a cold start, and the first few meters driven in SDI mode would irreparably ruin the emission balance.
But what specific guidelines for the engine start-up and departure process do the inspection regulations actually contain?
"Does it say 'As soon as the engine starts, it must be driven', or something like 'It must be driven no later than 5 seconds after the engine starts'?"

If, for example, the testing regulation stated "The vehicle must be driven between 2 and 5 seconds after starting," why isn't the VTG-open timer at least set to 2 seconds? Is it due to the carelessness of the VAG application engineers, with the mentality of "If drivers who start quickly damage their turbochargers, it's 99% of the time after the warranty expires, and the aftermarket industry needs to survive anyway?"

OK, I can already guess Bertil's answer: Today's emission measurement cycles no longer include a warm-up period for the engine after a cold start, and the first few meters driven as an SDI would irreparably ruin the emission balance.

Hello Ulf,
Basically, I agree with you, and I don't put any load on my turbocharger until a few clear seconds after the engine starts, and after a few gentle bursts of acceleration to build up the oil pressure, but:

Does it say 'As soon as the engine starts, it must be driven,' or something like 'It must be driven no later than 5 seconds after the engine starts'?

This is where it gets dangerous.
Your specified timer always applies.
If you switch off the engine while stationary, for example, when you are fully loaded with a trailer on a hill, this very timer can become a hazard because you have 'no' engine power, which can lead to a vicious cycle.
Furthermore, anyone who owns a garage with a steep driveway would be forced to poison the garage for a few seconds.

'Bertils' emission regulations will be another reason.

Due to the carelessness of the VAG application developers, following the motto 'If drivers with fast-charging capabilities damage their chargers, it's 99% of the time after the warranty expires, and the aftermarket industry needs to survive anyway'?

I don't see it that way; rather, it's the customers who complain about a significant lack of power when starting the car and that they can't get it out of their basement garage .

Best regards, Jochen.

Hi Ulf,

Sometimes I think you come up with worries that I would never even think of... Okay, there might be people who immediately floor the accelerator the moment the engine starts, but that's not what most people do.

"Just for fun, I once submerged an old oil pump in oil and powered it with a drill (okay, maybe you only do that once in your life, but I did it recently because I wanted to see how my 55-year-old BMW R25 oil pump compares to one from an ASZ [presumably a specific engine model]). Even at low speeds, it produces a significant oil flow. Of course, it takes more to build up pressure, but I didn't even check that. The oil line to the turbo wouldn't completely run dry either. So, I think for the average user, there shouldn't be any problems from this aspect..."

Jochen_145 wrote:

If you switch off the engine at the start, for example, when you are fully loaded with a trailer on a hill, this very timer can become a hazard, because you have "no" engine power, and this can lead to a vicious cycle.

. . . not endless, but only until I learn to wait for the timer before demanding torque.

Quote:

Furthermore, anyone who has a garage with a steep driveway would be forced to "poison" the garage for a few seconds.

Of course, in our environmentally conscious times, this is a "strong" argument.

Quote:

Customers who complain about a significant difficulty starting their car and being unable to get it out of their basement garage

I will probably never truly be able to put myself in the shoes of such anti-technology individuals .

Hey Ulf!

Why don't you simply install an oil pressure gauge with a sensor in the feed line to the turbo?

That should answer your question;-) even without getting too theoretical.
What if?

Best regards, Alex.

matthiasTDI96 wrote:

The oil line to the turbo will not completely dry out . So, I think for the average user, there shouldn't be any problems from that perspective...

Hi Matthias,

That seems to me just as much of a speculation as my scenarios .

majesty87 wrote:

Why don't you simply install an oil pressure gauge with a sensor in the feed line to the turbo?

... so that the branch is cut off at some point due to incorrectly estimated vibrations at Pmax? This will immediately cause a turbocharger failure, and the engine may also fail due to oil starvation and/or compressor surge.
No, thank you, that's too risky for me. I'd rather wait for answers from people who really know what they're talking about. And if no one responds, my loader won't break down because of that.

Okay, here's the translation:

"Now, with the turbocharger I've been working on so far, it was still possible to extract some oil."
However, that's speculation, and I agree with that.

This is a topic that I've also thought about quite a bit.
"I can at least share my experiences with my 1Z engine. The 1Z has two oil pressure switches: one at 0.3 bar for engine speeds below 2000 RPM, and another at 1.8 bar for engine speeds above 2000 RPM. Additionally, I have an aftermarket oil pressure gauge."
During a cold start, it can be observed that the engine runs for approximately half a second without oil pressure (as indicated by the warning light and pressure gauge), and then it takes another second for the oil pressure to build up completely.
"As far as I know, newer engines only have one pressure switch for high RPMs, and that's why you don't notice the delayed pressure buildup."

I don't think that's why your charger is broken;-)
And I didn't mean that as a permanent solution, but just to put your theory into practice.
Basically, you're waiting for someone else to do it so you can avoid the risk. X

I only don't understand one thing: If there aren't actually any increased cargo failures, why are you worried about the oil supply? It seems like everything is fine, so far...

Best regards, Alex.

majesty78 wrote:

So, you're essentially waiting for someone who has already done it, to spare yourself the risk;-)

He doesn't have to be driving around with a manometer attached to the oil line.
But if someone is knowledgeable about topics like engine lubrication, oil pumps, etc., and can accurately estimate when the oil flow stabilizes in the usual (TDI-VTG) components from the moment the engine starts, that would be sufficient.

Quote:

There's only one thing I don't understand: If there aren't actually any increased failure rates for the chargers, why are you worried about the oil supply? It seems like everything is fine, so far...

For example, BWT's published goal is that their chargers should last as long as the corresponding engine.
Therefore, in my opinion, any individual charger that fails before the engine or car is scrapped is a potential candidate for the category "killed gradually within the first x seconds after engine start," unless other causes are definitively established in each individual case, such as foreign objects being sucked in or reckless modifications.

The unresolved issue of premature charger failures is, in my opinion, definitely worth considering, even if it doesn't affect every third TDI.

Hi Ulf,

"Many people have probably struggled with these issues. It would be interesting to see the impeller speed during startup. Certainly, a supercharger operating at 200,000 rpm requires a higher oil volume than one operating at, say, 20,000 rpm. Here, the oil supply is also important for cooling and, above all, for damping vibrations (engine vibrations, the slightest parasitic movements, etc.). I think that at the low startup speeds, a thin lubricating film is sufficient, and it should still be present even after weeks of inactivity."

Here's another point to consider: In most cases, wastegate or VNT systems rely on vacuum-operated turbochargers that, without vacuum, operate at their minimum setting. Even in a small vacuum circuit, it takes a short time for the pressure to build up. In my case, for example, the check valve of the brake booster is "defective," so the brake is hard after a night, and the vacuum in the entire system is only available after about 5 seconds at idle (similar to what you're doing with the software, but I'm achieving it through my defective valve).

"When a driver pushes the engine to its limit with a factory-standard setup, the oil pump's flow rate at 2000 rpm (engine speed) is, in my opinion, within the range where adequate oil supply is ensured. At that point, the turbocharger is only operating at slightly above 50% of its maximum possible speed (as mentioned in the first paragraph)."

A neighbor has been using a technique since the beginning of owning his 3B with an AJM engine: he shuts it off with a strong burst of gas when parking (a habit from his carburetor engine 20 years ago :-/). After the engine was off, you could still hear the turbocharger whining. The first ATL (presumably a component) lasted over 100,000 km.

Unfortunately, my engine never seems to get the proper amount of MoS2 additive into the oil, and the check valve in my oil pressure regulator remains defective.

In short, what I want to say is that in the factory setup, it's designed in such a way that the ATL (presumably a component) cannot be easily destroyed by force, especially not quickly.

I think you're worrying about something that was already resolved a long time ago.

The loader itself actually has a built-in oil reservoir that allows it to start up immediately with lubrication during a cold start. Don't ask me how long it lasts, but you can try it out.

not without reason, a new automatic transmission fluid (ATF) cooler must be filled with engine oil before installation - precisely to prevent what ULFS mentally envisions .

greetings

Some drivers of company cars experience knocking directly after cold starts. The AFN turbocharger is still the first one with 420,000 km, despite a very high percentage of full throttle driving on the highway. The AJM, which also knocks both when cold and warm, had its ATL turbocharger break at 295,000 km. Is the LD (boost pressure) higher on the AJM than on the AFN? Curiously, these engines are virtually indestructible despite a lack of maintenance (50,000 km or more without oil changes). I personally always start my TDI first, then buckle up, and then I go.

ulf wrote:

OK, I can already guess Bertil's answer: Today's emission measurement cycles no longer include a warm-up period for the engine after a cold start, and the first few meters driven in SDI mode would irreparably ruin the emission balance.

This time, not ...

ulf wrote:

But what specific guidelines for the engine start-up and departure process do the inspection regulations actually contain?

The MVEG EU cycle does not include a warm-up phase. If the tester on the dynamometer falls below the prescribed speed for a certain period, the measurement cycle is invalid... -> restart.

Only the Asian cycles include a warm-up phase, which is even relatively long.

ulf wrote:

Does it say "As soon as the engine starts, it must be driven," or something like "No later than 5 seconds after the engine starts, it must be driven"?

I've linked to the cycle data before. You can find the speed profile as a function of time there.

As far as I remember, the speed should be around 4 km/h after 10 seconds. That should be enough time for the turbo to build up a safe oil supply.
In the US cycle, it reaches 3.6 km/h after 9 seconds, while in the Asian cycle, it reaches 2.9 km/h after 20 seconds. In the Asian urban cycle, it only reaches 2.8 km/h after 66 seconds.

However, the emissions are measured immediately. Therefore, even a warm-up phase is included in the measurement.

ulf wrote:

... But if someone is knowledgeable about topics like engine lubrication, oil pumps, etc., and can accurately estimate when the oil flow stabilizes in the usual (TDI-VTG) components from the moment the engine starts, that would be sufficient. . .

As soon as the engine reaches its idle speed (especially with modern engines).
In any case, you (or the EDC) will hardly be able to accelerate quickly enough to make the turbocharger "work hard".

The supply lines to the charger and the oil lines within the charger are now designed in such a way that they cannot run dry. This is a result of the technical advancements in automotive engineering over the past few decades.
While early loaders were extremely prone to certain issues, and the owner's manual had to explicitly mention that the oil flow to the loader might not "stop" immediately, this is no longer a major problem today due to the widespread use of loaders. Design improvements have been implemented to avoid such defects. Otherwise, loader manufacturers would hardly be able to avoid warranty claims.

I would be more concerned about the potential for sudden (and possibly uneven) heating of the charger components. This can significantly shorten the lifespan of a charger, even with adequate lubrication.

Bertil wrote:

In any case, you (or the EDC) will hardly be able to apply the throttle quickly enough to make the turbocharger "work hard".

(Finally, Bertil is joining in )

In other words, are today's VTG loaders "guaranteed to be fully resistant to premature ignition due to lubrication issues"?

Quote:

I would be more concerned about the potential for sudden (and possibly uneven) heating of the charger components. This can significantly shorten the lifespan of a charger today, even with sufficient lubrication.

. . . but not "thermally resistant to full-throttle ignition"?

Then, perhaps using the VTG off-timer still makes sense to ensure a gradual and safe warm-up phase for the charger, using "exhaust temperature control similar to that of an SDI engine"?
It would only be foolish if warming up after a frost-cold start takes significantly more time than the approximately 10 seconds I estimate for establishing a safe lubrication of the charger .

ulf wrote:

... In other words, are today's VTG loaders "guaranteed to be fully resistant to premature ignition due to lubrication issues"?

Okay, here's the translation:

"I'll leave it as it is, without adding 'guaranteed'."

Quote:

...but not "thermally stable for full-throttle, instant start"?

Not only after starting, but also after periods of heavy use, the turbo should be allowed a short "cooling-down" period.

Quote:

Then, perhaps using the VTG-Off timer still makes sense to ensure a gradual and safe warm-up phase for the charger, providing "exhaust temperature control similar to that of an SDI engine"? It would only be foolish if warming up after a frost-cold start takes significantly more time than the approximately 10 seconds I estimate for establishing a safe lubrication of the charger

.

So, you're definitely going to be all over that...