Laderpfeiffen nach Kaltstart | Posts 16+

I suspect the loader makes more noise when it's cold because the clearances are larger.

Okay, so I already knew that a Formula 1 car doesn't have a turbo, but a TDI with a broken turbo also wouldn't have one. I was just referring to the smoke effect that occurs when a motor sucks in hot oil, or when something like that gets into the hot exhaust - like you saw with those two Formula 1 cars in the last race.

Therefore: If the turbo is broken, you'll see it. Don't confuse it with a stuck variable geometry turbo (VTG) vane. That's usually fixable. In that case, the turbo isn't actually broken, it's just dirty, and that's a difference of 500 euros.

Driving an AFN or TDI without an air filter? Only do this if you have a panel air filter at home, otherwise I wouldn't recommend it.

Dirt, including that which passes through the air filter, is considered a major cause of failure in mass airflow sensors (MAF sensors).

garth.brooks wrote:

Dirt, including that which comes through the air filter, is considered a major cause of failure for Mass Air Flow (MAF) sensors

.

The dirt particles not only damage the mass airflow sensor (MAF), but also other components. In particular, the impeller wheels of the turbocharger and blade fractures are primarily caused by foreign object damage. Therefore, never drive without an air filter.

kapernaum wrote:

2. Theory: The exhaust system isn't warm enough yet. It makes sense that the resonant behavior of a heated metal is different from that of a cold metal. "But the noise is actually generated before the exhaust system, which you can clearly hear."

Not only does the temperature of the exhaust system change, but also the temperature of the turbocharger. And since the parts in our turbochargers are mostly made of metal (although there are sometimes silicone O-rings on the compressor side), the resonant behavior of the turbocharger also changes. Therefore, it is perfectly normal for a cold turbocharger/engine to whistle/sound different than a warm one.

hello again,

I meant something different when I talked about the exhaust temperature.

My theory:

The back pressure created by the exhaust system is a crucial element of noise reduction. When the system is hot, a specific mass of gas will have a specific...
(Larger) volume. This volume is much smaller when the system is cold. This results in lower exhaust back pressure, but the system becomes louder.

It disappears very quickly because the exhaust also heats up rapidly.

What are your thoughts on this?

The exhaust gas has roughly the same temperature from the beginning, at least at the cylinder outlet. Okay, until the end of the exhaust system, more heat is extracted during the warm-up phase than later. However, in relation to this, the temperature difference between the cold and the operating (hot) state of the metal is quite small. The resonant behavior of the hot metal (e.g., the turbine wheel) changes significantly compared to the cold state.

Hi,

On www.golf4tdi.de.vu, there is a sound file available for download.
Engine: ALH

The direct link:

http://members.void.at/wuze60/topf1.WAV

Greetings.
Thomas.

That's exactly what I'm hearing too. But it only lasts for 30 seconds, then the whistling stops.

The dirt particles not only damage the mass airflow sensor (MAF), but also other parts in the same way. In particular, the impeller wheels of the turbocharger, and blade fractures, are primarily due to foreign object damage. Therefore, never drive without an air filter.

Das man nicht ohne Luftfilter fahren sollte ist mir klar. Hätte auch vielleicht besser dazugeschrieben das das nur ein Versuch war wie er sich anhört und nicht ein dauerhafter Zustand. SSorry.
I've already mentioned this in another thread.