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Lately my petrol engine (2.4L V6, Audi A6 C6 '05) started to sound more like a diesel engine. It feels like, whenever I give the tiniest amount of gas, there is some knocking noise. However, let's say I revved it all the way up to 7000 RPM and don't press the gas, it doesn't make the noise anymore.

So, whenever I actually give it gas, it makes the noise. I just can't hear it when it's idle..

I've done a bit of research and it seems that the 'Timing chain tensioner' could cause something like this?

How far am I off? I still drive it to work everyday and I don't notice anything in terms of temperature, mileage or anything..

It seems that after 4-5KRPM it seems to fade away, but that could be because of the engine noise being louder than the knocking...

Any ideas?


Edit 1: Added recording from the inside, cold engine

Here's a recording when the engine was still somewhat cold, from inside the vehicle. It's fairly hard to hear..- but really focus near the end of a rev when the engine sound goes down a bit, the "trrrrrr" is still a bit audible.

I think you can hear it near the end of the recording, when I give it some gas and release a couple of times.. (0:42 - 1:05) https://vocaroo.com/i/s0UvkNFNYtwU (Sorry for my keychain, I didn't notice till later)

(Yes I know you shouldn't rev too much when it's still cold..)


Edit 2: When did this start?

I had hit the 'guardrail' on the highway with a speed of ~40KM/h (25MPH) with only the left side. This caused some slight damage to the radiator. The plastic covers on the side cracked which caused coolant to leak.

I drove the car roughly a quarter mile to a safe place and left it there. This may have caused some overheating but I doubt it.

After roughly 3-4 days after replacing the radiator and other damaged exterior parts, this 'ticking / knocking' has started.

I must note that there is one foam piece I couldn't fit correctly in between the front fender and the frame. The ticking could be a loose part hitting some other metal, as the engine is shaking.. but it's a tiny chance...


Edit #3: Added recording

https://youtu.be/lcbzG_nalJM

  • Which engine is in the A6? – Pᴀᴜʟsᴛᴇʀ2 Feb 17 '18 at 4:31
  • How many miles on the car? What's the service schedule been like? Can you provide a sample? – Ben Feb 17 '18 at 17:29
  • @Ben Roughly 250.000KM and service shedule is somewhat yearly, I've only owned it for a year and 2 months now. It has been to service atleast once every year. I've done a big service 3-4 months ago, changing almost all fluids, skipped belt as it was changed 2 months before I bought it and I only drove ±30.000KM on it since the change. Also, I'll try to record some of the knocking and put it in the question – Paramone Feb 18 '18 at 1:32
  • @Pᴀᴜʟsᴛᴇʀ2 2.4L V6, I've put it in my question now as well – Paramone Feb 18 '18 at 1:33
  • I had a car that ticked and knocked at all RPMs, and the cause was probably piston slap (VW 1.4 litre naturally aspirated engine). If you don't hear it tick at idle, it probably isn't piston slap. I would guess as well timing chain is the culprit here. Any temperature dependence in the noise? – juhist Feb 18 '18 at 12:42
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Several keywords in the question and subsequent comments caught my attention:

  • Ticking.
  • Sounds like a diesel.
  • Worse at cold start.
  • Can be heard even at idle.

I had all of these in a 2003 VW Golf 1.4 (the seller probably put oil via the spark plug holes to the engine immediately before the sale; otherwise I wouldn't have bought the car). My understanding is that the cause is piston slap.

If you can tolerate the sound and people making jokes about you having a dirty diesel car, just continue driving it. The resale value of piston slappers is really low. Eventually the engine will die an early death, but you probably knew this, the car having already 250 000 km.

I can't be 100% certain from the sound recording that it's piston slap (it doesn't sound to me like a major mechanical problem in the recording -- did you record with the hood open with the recorder in the engine bay? edit: no, the OP didn't, as stated in the question edit). My slapping was much worse than yours and still the car started reliably every day!

Just to be safe, I would ask a mechanic's opinion. If it's the timing chain, it should be fixed, especially if there's nothing else wrong in the car. Fixing piston slap for a 250 000 km driven engine is way too expensive.

This is what piston slap sounds like: https://www.youtube.com/watch?v=f_I8bc734_8

And in the engine I had a long time ago: https://www.youtube.com/watch?v=WLkyGaHzWQU

Even these sounds far worse than yours don't mean the car will immediately fail.

  • Amazing answer! I've checked both video's and the slap sounds a bit louder than mine. I don't think you can really hear it from outside of the vehicle, as far as I know. I haven't noticed anything in terms of fuel consumption / oil / anything else; so I doubt that it'll fail instantly. I'll try to get a better recording when I leave work in a few hours. – Paramone Feb 19 '18 at 13:54

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