Timing Chain rattle theory - hoping for Input

[bauerkraut]

I have a 2010 A6 3.0T that is a great performer other than the cold start timing chain rattle, with a twist...

The Symptoms:

On cold start, the chain will rattle for a couple of seconds at startup which I understand is 'normal'.

After those first couple of seconds the aggressive rattle stops, but will continue with a mild rattle off and on. If I just sit there and do nothing or even gently apply some gas, it will still mildly rattle away, coming and going. I'm not sure how long it will go, at least a minute or more, I don't want to extend the time it is rattling to test it.

I even waited for the choke to cut out and RPMs to drop, but still rattlin'.

Now for the twist --- If I simply turn the ignition off and restart the car, the rattling is completely gone.

Doesn't matter if I waited 5 seconds, 10 seconds, 30 seconds, etc. As soon as I turn the ignition off and restart the car, all rattle is gone.

Ideas:

This seems like evidence that the tensioners are fine. It's almost like a sensor or switch or ECU signal etc. did not wake up and do what it is supposed to until the car is restarted. Otherwise, what is it about simply restarting the car that gets the oil where it needs to be?

If it was about building oil pressure, engine temp, etc., then it seems like just sitting there and letting it idle would fix that. For me, sitting there longer at idle does nothing. The trick is just turning off the car and restarting.

Once I have completed the start / restart ritual, rattle doesn't occur again the rest of the day (so far), even if the car has been sitting for 8 hours or more.

I know I've read of others on here who changed tensioners and then the problem returns not long after, indicating that the root cause likely never was the tensioners to begin with.

Has anyone figured out a sensor or other part of the system that may really be the root cause?

Appreciate any input, thanks!

[estomax]

My car had very very similar symptoms with the rattle coming and going like you're describing. This in my opinion is a classic timing chain tensioner failure, which i ignored and hoped it would last longer and get 'worse' before i did the job. I ended up waiting until one morning the car started up and started running like complete garbage. What ended up happening is the plastic on one of my tensioners failed completely and skipped a couple of teeth of timing. I was lucky that i did not damage the valves and was able to buy new tensioners and replace them as a first time job in about 7 hours.

my hypothesis is that the failed tensioner piston can get enough oil pressure behind it to not rattle most of the time, but sometimes when it relaxes and oil pushes it out at a slightly skewed angle at next start, the chain can rattle. more oil pressure sometimes fixes it (revving).

i've only had my tensioners replaced for about a month but the noises from that are all gone now.

[bauerkraut]

Thanks for the feedback @estomax

First question, if you don't mind sharing is where did you get the work done and do you mind sharing the cost? I didn't pay that much for my A6, but I do really enjoy the car. I need to think about the cost benefit aspects.

Per another thread, I can mitigate most if not all the cold-start rattle by adding more oil above the dipstick max.

https://www.audizine.com/forum/showt...0#post14951120

Running about a quart high mitigates cold start issue greatly. But I would like to 'fix' the issue depending on cost / benefit.

My main curiousity though has to do with why the start / restart cycle eliminates the chain rattle altogether. Per your experience, I will likely run higher oil levels for now to lower the chance of what happened to you on startup, but if there is another root cause such as a sensor, etc., then of course that would be an ideal and hopefully less costly fix.

Thanks!

[bauerkraut]

I was lucky that i did not damage the valves and was able to buy new tensioners and replace them as a first time job in about 7 hours.

Reading this again, looks like you did the job yourself? I'm probably handy enough to do it with a proper guide, although my engine is the 3.0T. I may just roll the dice, but of course it's nagging to know that the problem is there. Thanks again

[estomax]

yeah i did it myself, there is a video on youtube and i took some extra clips during the job that i should throw up as a secondary / shorter guide for the job too.
https://www.youtube.com/watch?v=ZAWsKChptvU

be sure to buy the camshaft locking tools too, something like this:
https://www.ebay.com/itm/29263685374...item44228405f4

i am fairly sure the 3.0 is similar but check other guides over google/youtube to verify. Very much a doable job if you're at all handy and have the right tools. I also didn't pay much for my car, hence taking it to a mechanic would have cost as much as the car cost me 4 years ago, so no thanks on that.

you could also throw heavier oil in there, like 10w40 or 5w40 if you're still running 5w30.

if you take your intake manifold off you will have much more room to work, likely you will have to take your supercharger off to get enough space to comfortably do the back of the engine work. If that stuff has never been off your PCV hoses and other brittle will likely break. I have replaced my PCV hoses already previously due to this, not difficult, just an extra part to buy.

[bauerkraut]

Great info @estomax, thanks again. I did go to 5w-40 with no apparent benefit, but the higher oil level does help.

I honestly think the tensioners are fine if they just had the right amount of oil up there on cold start. To me, that is the root cause. Although this is a C7, I believe this guy is on to the answer, or at least closer -- https://www.youtube.com/shorts/4JG5XksgWFk

[King_Tutt]

Personally if it was my car, I would first do the upper tensioners since they are easiest to get at without dropping the engine.
The video that you posted makes me wonder if that valve is sticking or maybe air is getting stuck in the tensioner until the restart.
Either way keep us informed about what you do and if anything changes

[bauerkraut]

Personally if it was my car, I would first do the upper tensioners since they are easiest to get at without dropping the engine.
The video that you posted makes me wonder if that valve is sticking or maybe air is getting stuck in the tensioner until the restart.
Either way keep us informed about what you do and if anything changes

I've confirmed that beyond initial startup all of the noise is coming from the driver's side timing chain. I'm going to start there and replace that upper tensioner and guide and see how things are looking / sounding afterward. Hopefully no issue with the chain itself.

[G-Can]

I've confirmed that beyond initial startup all of the noise is coming from the driver's side timing chain. I'm going to start there and replace that upper tensioner and guide and see how things are looking / sounding afterward. Hopefully no issue with the chain itself.

although I have a 3.2, with tensioners done 3-4 years ago, I do have occasional rattle, but same rattle as you describe it, car would actually start rattle free or minimal, but will continue to faintly rattle for a while.

and shutting down the car as you descirbed, also, completelly stops the rattle upon restart. I figured this out a while back, and this topic just reminded me.
I have also realised that keeping oil levels at max or bit over max mitigates the rattle drastically, to the point it happens rally rare.

ALso, another thing that drastically helps weith rattlem, is if the car cranks a second longer then instantly firing. When I had a weak battery, car would crank for long half second or second longer, and it would NEVER rattle.

It is all about oil pressure and why sometimes tensioners dont get proper oil pressure, and I say it is one thing alone that is a root cause of all failures:

Variable Timing Solenoid

[a1dan_87]

What worked for me to stave off the rattle was switching to LiquiMoly oil and changing it VERY aggressively. If I went over ~2500 miles between changes my rattle would come back and get worse the longer I went. Tried Valvoline, Pennzoil, Mobil1, etc, and LiquiMoly helped the most.

But it still rattled *some*, and that was only a bandaid on a bullet wound as I didn't have the money to fix it before I sold the car.

As far as I know, all chain driven engines rattle on cold starts. But it shouldn't stick around

Sent from my LE2127 using Audizine Forum mobile app

[G-Can]

No they don't. Mine rarely rattles. Once in 10 starts, when it's very cold outside (I live in penguin land Canada) sometimes if as I said, oil is not at max. But when it's very cold, car usually cranks bit longer and that brings oil pressure quicker then when its warm.

These are just poorly on purpose badly designed engines.

[bauerkraut]

although I have a 3.2, with tensioners done 3-4 years ago, I do have occasional rattle, but same rattle as you describe it, car would actually start rattle free or minimal, but will continue to faintly rattle for a while.

and shutting down the car as you descirbed, also, completelly stops the rattle upon restart. I figured this out a while back, and this topic just reminded me.
I have also realised that keeping oil levels at max or bit over max mitigates the rattle drastically, to the point it happens rally rare.

ALso, another thing that drastically helps weith rattlem, is if the car cranks a second longer then instantly firing. When I had a weak battery, car would crank for long half second or second longer, and it would NEVER rattle.

It is all about oil pressure and why sometimes tensioners dont get proper oil pressure, and I say it is one thing alone that is a root cause of all failures:

Variable Timing Solenoid

Really appreciate the confirmation G-Can. It's not encouraging that you still have rattle even after having the tensioners done, but on the 3.0T at least the upper guides look so flimsy that they are bound to break down at some point. And yes, it's a flaw that they should have really done something about.

That said, for a 13 year old car I'm very happy with the A6 Quattro overall. It's going to cost me about $500 bucks between parts and tools that I don't currently have, and some angst of potentially messing something up royal, for me to replace the drivers side tensioner, but I'm hoping I will get some peace of mind soon after.

I'm also changing out the oil filter at the same time. So I won't get a data point on that but will at least eliminate it as a potential contributor. I'll update when I do the tensioner replacement.

Thanks Again!

[bauerkraut]

What worked for me to stave off the rattle was switching to LiquiMoly oil and changing it VERY aggressively. If I went over ~2500 miles between changes my rattle would come back and get worse the longer I went. Tried Valvoline, Pennzoil, Mobil1, etc, and LiquiMoly helped the most.

But it still rattled *some*, and that was only a bandaid on a bullet wound as I didn't have the money to fix it before I sold the car.

As far as I know, all chain driven engines rattle on cold starts. But it shouldn't stick around

Sent from my LE2127 using Audizine Forum mobile app

Good advice on the oil for sure. As far as chain rattle, I can confirm after owning 3 different BMWs with 3.0 M54 engines there was never a hint of chain rattle. But that engine is also a straight 6 vs. a V and I'm sure much simpler in the timing chain design.

[arjun90]

The way I approached it was, before I start the car, I simply hold the start/stop button without putting my foot on the brake. A couple of seconds later, I start the car and voila - no rattle. One in 5 cold starts I get 1-2 seconds of rattle, other than that its fine even at 163,000 miles

Good advice on the oil for sure. As far as chain rattle, I can confirm after owning 3 different BMWs with 3.0 M54 engines there was never a hint of chain rattle. But that engine is also a straight 6 vs. a V and I'm sure much simpler in the timing chain design.

[G-Can]

The way I approached it was, before I start the car, I simply hold the start/stop button without putting my foot on the brake. A couple of seconds later, I start the car and voila - no rattle. One in 5 cold starts I get 1-2 seconds of rattle, other than that its fine even at 163,000 miles

wait, what? does the car crank but doesnt start if the foot is not on the brake? I never tried this, but if that is the case, that would definitelly help as it will build up oil pressure.

[estomax]

hmm.. my car definitely starts even if the brake is not down, no way to just dry crank.

[arjun90]

I'm not sure why your's is different. On both my Q5 and A6, I need to press the brake while I press start engine to crank the engine

hmm.. my car definitely starts even if the brake is not down, no way to just dry crank.

[arjun90]

I am very sure this is not a placebo effect. I've done this on the Q5 and the A6, and both times the rattle is non-existent at cold start by starting the car this way. Sometimes, just for laughs I skip this part just to hear the 1-2 second rattle on a hot and humid day. The only annoying part is that I am always reminded that I have a car containing timing chains with sh!tty plastic guides, lol.
Fortunately, I have yet to experience over 3 seconds of timing chain rattle. I just replaced my vacuum pump and the car has quieted down even further.


I definitely encourage everyone to just press start engine during a cold start without putting your foot on the brake pedal. If you put your ear to the engine bay, the car's ABS and ECU makes a characteristic noise which is 100% normal - interestingly, something tells me this allows a valve to open and allow a little bit of oil to release over the guides prior to startup. There is always residual vacuum in the system to allow a little bit of pressure and physics to take place internally within the engine. I was pleasantly surprised by the residual vacuum within the system even with the car off (when disconnecting my vacuum pump).

wait, what? does the car crank but doesnt start if the foot is not on the brake? I never tried this, but if that is the case, that would definitelly help as it will build up oil pressure.

[G-Can]

I allways do that, as a habit. Flip the key to/press the start button, to get the juices going through the car, usually, Ill flick it, put my seatbelt, and then start the car.
just got used to that since driving old diesel that had heaters.

I still find that high oil levels are best deterent of rattle. Or if there could be a way to make these cars crank for half a second/second to actually turn the engine and build up oil pressure. Thats crucial.

[arjun90]

Does anyone what values to look for in VCDS in Group 93? I'm not sure why Camshaft Adjustment shows units in percentage when it should be in degrees

[arjun90]

I definitely recommend an Engine Flush at least 1-2 times a year depending on how its driven

[arjun90]

Its funny - its been over a week since I did an engine oil flush and the rattle has been kept at a minimum at startup. Also, oil consumption has been reduced drastically.

[G-Can]

Can you explain what exactly you mean by engine flush?

[arjun90]

I used Liqui Moly's Pro-Line Engine Flush and drained out the old oil and oil filter after letting it circulate for 10-15 mins. I then used Mobil-1 0W40 along with a new oil filter and let that circulate for 10-15 mins. I drained out the oil along with the oil filter and whatever that was left behind from the engine Flush and used used 7 liters of Motul 300V Performance 5W40 oil along with a new oil filter. So far, there has been very little to no oil consumption (despite being in traffic, 90+ degree weather) and driving the car daily almost every day for a little over a week. I did have a one day gap, but the cold start rattle was only present for a split second. I haven't experienced any rattling with a warm engine either. Sure, this costed me a lot of money, but I am convinced that mixing oils (when topping off in between oil change intervals) despite being the same weight is not a good idea for these overly sensitive engines.

Can you explain what exactly you mean by engine flush?

[G-Can]

I used Liqui Moly's Pro-Line Engine Flush and drained out the old oil and oil filter after letting it circulate for 10-15 mins. I then used Mobil-1 0W40 along with a new oil filter and let that circulate for 10-15 mins. I drained out the oil along with the oil filter and whatever that was left behind from the engine Flush and used used 7 liters of Motul 300V Performance 5W40 oil along with a new oil filter. So far, there has been very little to no oil consumption (despite being in traffic, 90+ degree weather) and driving the car daily almost every day for a little over a week. I did have a one day gap, but the cold start rattle was only present for a split second. I haven't experienced any rattling with a warm engine either. Sure, this costed me a lot of money, but I am convinced that mixing oils (when topping off in between oil change intervals) despite being the same weight is not a good idea for these overly sensitive engines.

We can't fix what's broken from factory.

Rattle is gone because of fresh oil in the engine and level to the max.

I've done that process what you'd done, and had zero noticeable difference.

In my head, I describe it as having two showers in a row.
Will you be cleaner or smell fresh longer?
Not really. Negligible. Especially if you don't put deodorant on haha

[arjun90]

True, we can't fix what's broken, but we can definitely buy some time if the situation hasn't gotten worse already. Audi should have definitely considered the long term implications of their flawed designs, but then again we are talking about the VW Group here. This could very well be my last Audi / VW

We can't fix what's broken from factory.

Rattle is gone because of fresh oil in the engine and level to the max.

I've done that process what you'd done, and had zero noticeable difference.

In my head, I describe it as having two showers in a row.
Will you be cleaner or smell fresh longer?
Not really. Negligible. Especially if you don't put deodorant on haha

[G-Can]

I'm pretty confident I'm going different route after this one.

Kia Stinger is my favorite, Genesis G50/70, there are some great cars out there that will be waaaaaay more reliable then crapshoot overenginnered (read:over complicated garbage) Audi.

[mstc21]

Hi Bauerkraut, I have EXACTLY the symptoms you describe with my 2009 B8 S4 avant, 114k miles. I have never heard anyone speak of the occasional in and out light rattle for approx 1 min after startup before. It happens on some startups, not on others. Currently considering options, including the potential installation of an oil pressure check valve, along with 0w40 kept full to the brim (currently running 5w30 and not always full up). Have you made any progress since this thread? Thanks, Mike.

[Avantly]

Engine flushing especially on something that hasn't had it done before is just begging for sludge to be broken free and lodged somewhere that causes catastrophic damage. There is absolutely no use case nor no valid data showing any benefit of "engine flushing" on an engine that has oil changes at even remotely decent intervals.
Never discount the startup rattle as being possibly caused by the check valves in the valley no longer acting as check valves. Some believe that these check valves not sealing is the primary cause for early tensioner failure but I have no personal evidence to support this.