Combustion noise, temperature-dependent?

Hello everyone,

I mentioned earlier about a "ringing sound" that can sometimes be heard in the combustion noise, especially at low loads and around 1500-2500 RPM.

I've continued to observe it, and I think it doesn't occur when the temperature is around 8 degrees Celsius, as it was this morning, but it does occur when the temperature is around 15 degrees Celsius, as it is this afternoon, under otherwise identical conditions.

What do you think - is there a slight dependence of the combustion sound on the temperature? Does that make sense? Has anyone else noticed something similar before?

As I said, this effect is very weak – and it could also be caused by resonances in the exhaust system or vibrations in the front bodywork, which temperature might also affect.

Best regards,

Jan.

Hi Jan,

My engine's sound isn't always the same either - sometimes it's a bit softer, and sometimes it has a slight metallic clatter (in both cases, after it's warmed up).

I think that depends on several factors.
"For example, due to the turbocharger: after a cold start, my variable turbine geometry (VTG) sometimes gets stuck, and when I accelerate moderately from a low RPM, there is no boost pressure. This results in a noticeable 'knocking' sound, which is absent when the VTG is functioning correctly."

Furthermore, the start of fuel injection is regulated based on engine load and temperature. In other words, until the engine reaches its operating temperature, the point at which injection begins will vary depending on the external ("cold start") temperature, even with the same load, which, as is well known, can significantly affect the engine's sound.

I haven't yet made any "detailed" noise observations that depend on the outside temperature...

Hi Ulf,

You're probably right... I'm probably being a bit too sensitive about the noises, both the ones that indicated the leak back then and the ones the clutch is making now.

But the explanation about the start of the hammering makes sense, as does the description that hammering sounds different, because that applies to the noises I'm hearing. So, everything is normal, and there's no reason to worry .

Best regards,

Jan, who wants to address the issue with the boost pressure gauge as soon as possible.