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Old 16th December 2020, 05:30 PM
Markiii Markiii is offline
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Default Is my S8 borked

Been having a few issues of late which I'm not sure if they are linked, but the latest investigation results have me concerned

Would appreciate some advice as to how to proceed. Apologies for the mega long post but I thought it worth giving the full picture


All started at the back end of October

Due to lockdown/working from home its barely moved all year and even since October has probably done less than 200 miles.

So following a prolonged period of inactivity I jumped in to go to the gym and tried to start. absolutely nothing didn't even try to turn over.

suspecting a flat battery i used my jump pack and while it struggled a bit it did start.

Got back from the gym and put the battery on charge

que repeat performances over the next few days only cured by leaving permanently on charge.

However we now started to develop a very odd issue that whilst it wouldn't even try to turn over if you held the key in the start position for 10 seconds it would miraculously fire up as per normal.

Once running it all sounds fine,

Note from this point forward the car has only been driven very short distances for diagnostic purposes


Suspecting a goosed battery I popped a new one in and hoped that would be the end of my issues.

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Alas no it seemed to behave for a few days but quickly returned to the situation above. However the starting issue was now intermittent seeming to occur when the engine was cold, but be fine when warm.

I then decided to change the ignition coils, more because I had it on my list of maintenance items than anything else, but I thought I may get lucky and find it was also the issue. 8 NGK coils were procured and whilst its felt noticeably livelier in use the starting issue remained.

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Around this time I noticed I was losing coolant. I've yet to find any obvious signs of a leak so braced myself for needing to to do the oil cooler pipe.

Whilst researching this I elected to do an oil change, reasons being twofold, first it was due and second I wanted to see if there were any signs of the missing coolant.

Good news or so I thought, the oil came out as expected, dirty but no signs of coolant.

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The starting issue continued

This time I even noticed electrical smoke coming from the wheelarch on one occasion. (so far this has been a single occurence)

Note the car has only moved on my drive since this as I don't trust it until all is resolved.

My next thought was ground issue. On forum advice I have located the often problematic junction box and it seems in good order (see attached photo)

12.x volts apparent both at the battery and the junction box when not running and 14.x volts when running suggest to me that both battery, cabling and alternator are not at fault.

However at this point we started to notice a mechanical clatter at startup. Only at startup as it immediately vanished and the car idles and revs smoothly thereafter.

It sounds like a very loud heatshield rattle but seems to be coming from the alternator area. So far no joy in tracking this down.

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Today was supposed to see another attempt at finding the culprit. due to the clatter I mentioned I decided to check the oil level on the off chance it was somehow low and causing the issue.

And thats where I get really concerned. The oil on the dipstick looks like chocolate milkshake

The filler cap likewise.

I should note that at no point through this saga has there been any sign of oil in the coolant tank.

Dropping the oil did nothing for my mood as the bucket rapidly filled with more milkshake than oil.

I measured and rather than 8 litres its more like 9.5, which both explains where the coolant has been going and due to the excess volume can not have been doing the engine much good.


Note VCDS has yielded no error codes other than the parking sensors and radio missing which was as expected throughout muliple logging attempts
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So where next?

Is it possible that the oil cooler pipe is responsible, in which case proceeding to change it may solve the issues, or am I flogging a dead horse, is it likely to be something more serious?
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  #2  
Old 16th December 2020, 09:31 PM
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steamship steamship is offline
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However at this point we started to notice a mechanical clatter at startup. Only at startup as it immediately vanished and the car idles and revs smoothly thereafter.
That is the dreaded 'death rattle' which has been mentioned on the forum over the years. The culprit is the chain tensioners, and the 'chocolate milkshake' has probably made the issue with them worse. MJ can give a very detailed explanation, but from what I've understood of it, they have an oil filter which gets blocked and eventually the pressure destroys the filter which in turn destroys the o-rings inside the tensioner and after the engine is switched off, it loses the oil pressure keeping them in situ, and you then get the rattle at startup.

From what you've written, you only heard the rattle after noticing the 'chocolate milkshake', and with the excess volume (regardless of content), it sounds like that might have caused the tensioner issue.
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2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts

My DIY jobs - Replaced alarm horn, Replaced Coolant Temp sensor, Updated RNS-D firmware, Installed Reversing Camera and Digital TV, Dashcam Installation, Retrofitted Rear Blinds, Auto-Dimming Rear View Mirror, Chrome Boot Struts

Sold! 2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights

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Old 17th December 2020, 07:22 AM
MikkiJayne MikkiJayne is offline
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The milkshake will be a failed oil cooler as that is the only place oil and coolant are in the same place, other than the head gasket which neither I nor Ian have ever seen fail. Changing the oil cooler is the same as changing the oil cooler pipe since they're both in the same housing. A genuine cooler is about 200 and still available new as it is shared with the D3. Aftermarket versions are also available.

Sean is spot on about the tensioners and the milkshake could well have caused the failure. Its usually only the driver's side which rattles due to the design of it. The simple way to check is to pull the cam cover and turn the engine over by hand from the crank pulley. If the 'cold start pin' is jammed because it ate the filter, the inlet cam will jump forward just before TDC and the chain becomes slack, then as you continue to turn the engine the chain tightens up again and the inlet cam moves again. The cam jumping and the chain going slack are the cause of the noise. On a mature engine with >120k miles on it this really does need investigating because if the chain guides are worn (which they will be at that mileage) the chain slapping on them can break them and then worse things happen.

New tensioners are still available for 650 each. There's a chap in Lithuania who rebuilds them for 70 each but I haven't had a chance to try him yet, and there are new German aftermarket units available for about 250 iirc, although I haven't tried those either. Chinesium ones are garbage obviously.

Starting problems are usually one of three things - F125 is failing, junction box is corroded, starter interlock relay is full of water. Given that you've seen smoke from the wheel arch I would be inclined to remove the junction box to clean and inspect the starter cables. Its not uncommon for them to corrode inside the grease as moisture still gets in. The box is still available afaik and isn't expensive.
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Old 17th December 2020, 08:51 AM
Markiii Markiii is offline
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thanks guys

MJ tbh getting as far into the engine as the tensioners is beyond my comfort level especially as my garage isn't big enough to leave the s8 in overnight whilst in bits.

would you be able to fit me in to get these things done any time soon?
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Old 17th December 2020, 09:22 AM
MikkiJayne MikkiJayne is offline
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Probably January. I'll pm you later
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Old 17th December 2020, 09:24 AM
Markiii Markiii is offline
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fabulous ta
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Old 17th December 2020, 10:48 AM
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steamship steamship is offline
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If the 'cold start pin' is jammed because it ate the filter, the inlet cam will jump forward just before TDC and the chain becomes slack, then as you continue to turn the engine the chain tightens up again and the inlet cam moves again.
You've just answered something I've wondered about for a while. I have the 'death rattle' on mine, but not all the time, and could never figure out why.

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Originally Posted by MikkiJayne View Post
There's a chap in Lithuania who rebuilds them for 70 each but I haven't had a chance to try him yet.
If this is the same person we discussed some time back, I never got anywhere with them either. The initial problem was the person advertising the service wasn't the person doing it, there was an issue about how to pay for them, and when I got into discussing the logistics of shipping, it all went quiet.
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2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts

My DIY jobs - Replaced alarm horn, Replaced Coolant Temp sensor, Updated RNS-D firmware, Installed Reversing Camera and Digital TV, Dashcam Installation, Retrofitted Rear Blinds, Auto-Dimming Rear View Mirror, Chrome Boot Struts

Sold! 2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights

My DIY jobs - Fan Jet Windscreen Washers, Retrofitted Electric Side Blinds
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Old 17th December 2020, 11:17 AM
MikkiJayne MikkiJayne is offline
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You've just answered something I've wondered about for a while. I have the 'death rattle' on mine, but not all the time, and could never figure out why.
Do you remember the spring-loaded pin I showed you when you were here pre-Cornwall meet? That is designed to lock out the cam-timing aspect of the tensioner, so that the first thing the mechanism does when the engine starts turning is pump up the tensioner pressure. Only once it has pressure does it release the cold-start pin, which then pressurises the rest of the mechanism. In the driver's side tensioner the start pin is at the bottom of the assembly so when it eats the gauze filter, the little bits of stainless steel wire drop down in to the bottom of the mechanism and go through the start pin, jamming it open. On the passengr side, the pin is at the top so the wire just sits in the bottom of the tensioner without causing any damage. That means that on cold-start with no oil pressure, the tensioner has to receive more oil to get tension on the chain than it would if it were locked.

How long it takes for the tensioner to lose pressure depends on the state of the rubber o-rings inside it, and also the health of the oil retention valves under the valley cover plate. Usually after an initial cold start of an otherwise healthy engine, there is sufficient pressure for it not to rattle again that day, possibly even the next day, but after a couple of days the pressure has decreased sufficiently that the force from the chain of turning the cam pushes out any residual pressure and so it rattles until oil pressure is built up.

On really bad ones, they rattle on every startup. I had a look at one a while back which did this, meaning the gauze has gone through the tensioner and the oil system is sufficiently worn or full of burned crud from lack of oil changes that the seals in the tensioners are completely shot and can't maintain pressure at all.

Theoretically, one could make an interlock system which locks out the crank position sensor signal until oil pressure is achieved. That way, the engine would spin on the starter until it gets pressure, then fire up. I'm not sure how much of a delay that would cause to startup - I guess it would depend on how much pressure the oil system retains, plus it would place a heavier load on the battery. But, the plus side is that it might sound like a Veyron which appears to do something very similar

Veyron startup

This is a get-round-to-it project which I may have a go at simply to see if it works. Its certainly cheaper than changing the tensioners!

Quote:
Originally Posted by steamship
If this is the same person we discussed some time back, I never got anywhere with them either. The initial problem was the person advertising the service wasn't the person doing it, there was an issue about how to pay for them, and when I got into discussing the logistics of shipping, it all went quiet.
Thats disappointing. I was really hoping to see how he was managing to disassemble them.

There is the German aftermarket option, but thats a fairly expensive experiment, plus they don't have a separate unit for the 3.7 which is a different part number.

It would be much easier to just replace the damn things with a simple chain tensioner and code out the cam timing adjustment Thats a bit beyond 3d printing though.
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Old 17th December 2020, 04:45 PM
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steamship steamship is offline
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Quote:
Originally Posted by MikkiJayne View Post
Usually after an initial cold start of an otherwise healthy engine, there is sufficient pressure for it not to rattle again that day, possibly even the next day, but after a couple of days the pressure has decreased sufficiently that the force from the chain of turning the cam pushes out any residual pressure and so it rattles until oil pressure is built up.
This is the way mine currently is, but for the majority of this year I have only being going out in the car once a week, and that's only a four mile round trip with a stop in it, so not very healthy at all for it.

Quote:
Originally Posted by MikkiJayne View Post
This is a get-round-to-it project which I may have a go at simply to see if it works. Its certainly cheaper than changing the tensioners!
Sounds intriguing and definitely agree about the price of the tensioners. Maybe another service to offer the D2 owner.
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2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts

My DIY jobs - Replaced alarm horn, Replaced Coolant Temp sensor, Updated RNS-D firmware, Installed Reversing Camera and Digital TV, Dashcam Installation, Retrofitted Rear Blinds, Auto-Dimming Rear View Mirror, Chrome Boot Struts

Sold! 2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights

My DIY jobs - Fan Jet Windscreen Washers, Retrofitted Electric Side Blinds
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Old 18th December 2020, 02:58 AM
spannerrash spannerrash is offline
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I changed both my tensioners 3 years or so ago. Passenger side was not bad at all but I changed it anyhow. Drivers side rattled like a bugger. Oddly the screens were intact in both of them. Luckily no broken slides at all.
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