Engine Noise When Shutting Off

'I recently got a Seat Ibiza TDI with 81 kW, manufactured in 2000. I've noticed that it makes noises when I turn off the engine. It seems like the noise is coming from the turbocharger. Specifically, even after the engine is off, the turbo continues to run. Is it normal to hear it running so noticeably? I didn't notice this in my old Golf III TDI. Also, I'm not always turning off the engine immediately after full acceleration. The noise occurs consistently. Has anyone had experience with this?'

Hi.

My car also makes a quiet whirring sound after I park it.
Two potential sources come to mind: the charger (alternator) and the generator. The latter has a freewheel mechanism that also makes a slight noise (test: remove the belt, manually rotate the generator, and then hold the wheel still).

If the noise is clearly audible, you could try a different test.
Start the engine, immediately turn it off again, and pay attention to the duration of the sound.
Then try it with the alternator regulator cable disconnected. If the noise is now clearly longer, it's coming from the alternator because its kinetic energy isn't being converted into battery charging, so it continues running for a longer time.

I'll try it out at my place sometime too.

I initially thought it might be related to the free-flow exhaust system, but it's definitely coming from the turbocharger area. I'm surprised I didn't notice it in my Golf before, or maybe it didn't have one. I'll probably visit the dealer sometime soon. I have a used car warranty, so I'll report back what he tells me.
See you then.

Hi.

Quote:

It definitely comes from the Turbo direction. I'm just surprised that I didn't notice it in my Golf back then, or whether it didn't have it. I'll probably visit the dealer sometime soon. I have a used car warranty, so I'll report back what he tells me.

If the trip to the dealer is longer than 5 km, I would consider it a waste of time and money, because the likely response will be something like, "as long as there is no defect in performance, the charger is fine."

A more precise (and independent!) check would be possible with a boost pressure gauge.
But why would they install a standard instrument to monitor a (relatively vulnerable) function that the TDI "relies" on – that would just create even more annoying questions...

Hi Ulf,
'Hey, did you also disconnect your EGR valve? I found out that the turbo only continues to spin for a while after I turn off the engine if I disconnect the EGR. I reconnected it just in case. It might be better for the turbo. I think that with the EGR disconnected, the turbo might have higher idle RPMs because the pressure in the exhaust manifold is higher, since the EGR doesn't direct exhaust gases into the intake manifold. This probably causes the turbo to spin faster at idle, and therefore continue to spin for a longer time.'

Hello everyone!

[quote='schroederliese']Hi Ulf,
Think about whether the turbo, with the EGR disconnected, might have more RPM at idle, because the pressure in the exhaust manifold is higher since the exhaust gas recirculation system isn't directing exhaust gases into the intake manifold. This would likely cause the turbo to spin faster at idle, and therefore run longer after the engine is switched off.[/quote]

Interesting theory! It could also be a possible explanation for faster throttle response with a disabled EGR system, as it would then provide more exhaust gas for the turbocharger.

Regarding the noises you hear after turning off the engine, I only know of a hissing sound coming from the air conditioning system.

Regards,
Udo.

schroederliese wrote:

Hi Ulf, Hey, have you also disconnected your exhaust gas recirculation (EGR) system? I found out that the turbo only continues to run for a while after you stop the engine if you disconnect the EGR. I reconnected it just in case. It might be better for the turbo. I think that with the EGR disconnected, the turbo might have higher idle RPMs because the pressure in the exhaust manifold is higher, since the EGR doesn't direct exhaust gases into the intake manifold. This probably causes the turbo to spin faster at idle, and therefore continue to run for a longer time.

Hi.

"Recently, I've also been experiencing about 0.05 bar of pressure in the engine at idle, even with a faulty AGR (Exhaust Gas Recirculation) system – but only when the engine is warm! When the engine is cold, the oil is probably too thick to allow the turbocharger to start with such a small amount of exhaust gas flow at idle."
However, even with a hot engine, the pressure drops to "zero" within approximately 1 second after it's turned off. And I simply believe that for these "few revolutions of the turbocharger," the oil in the bearings is still sufficient.

Furthermore, if a problem were to develop in the charging or storage system, the warm idle charging pressure, due to its sensitivity, should ideally decrease first.
As long as nothing like that is observed, I will not repair my EGR valve again .

It's quite revealing, having a boost pressure gauge like that .

Hi,

I think I hear the exact same noise on mine.
Seat Leon TDI 110 hp. Has a faulty AGR valve, which causes the turbo to be audible.
It runs noticeably lean, but only when the engine is warm.
That's why I 'repaired' the AGR again.

Is this only the case with Seat?

Let's try a different question:
Do we still need to add 'turbo' to everything these days?
Should you let the engine run for a while before turning it off?

Best regards, Achim.

Hi.

Quote:

Does one still need to adjust the turbo nowadays? Should you let it run before turning off the engine?

If you drive 5 km at full throttle uphill on a highway, then brake hard and turn into a parking lot, and immediately turn off the engine, the turbocharger will still be almost red-hot, while the oil circulation inside it comes to a standstill.
Then the oil in the charger's reservoir will burn and leave a layer of oil sludge. Five (?) such occurrences, and the charger will seize up - in my opinion, even a supplementary radiator fan controlled by the engine computer won't help in that case.

So, drive more cautiously for the last few minutes (so that the charger can cool down using the circulating oil), and then you can turn off the engine immediately after about 3 seconds of idling.

The newer TDI engines have a throttle valve located in the intake manifold. Perhaps that's causing the unfamiliar noise!

It only blocks the flow channel when it's turned off.