Engine.... Heal thyself?
 

2006 A8 4.2 140K miles. Bought two years ago and love the car. First thing I observed on pre purchase inspection was no click clack of the cam tensioner chain on cold startup. This continued to be true. A few oil changes later it started clacking. I used Mobile One 5-30 not realizing it was not 502 spec and after the first year it's been clicking in the morning. The last few oil changes, I've been using 0-40 Mobile One and hoping that the problem might "go away".

It's my understanding there is an anti bleed back valve which is supposed to hold oil up in the cam adjuster. Further, that using wrong oil causes the valve to let the oil bleed down? My thinking is the wrong spec oil my clog it and in fact, have the opposite effect. Can someone explain what it is about the 502 that allows oil to stay up in the cam adjuster?

Could be the chain tensioner the plastic wears down. Makes the chain rattle.

I know exactly what the noise is. This is my fourth A8. I was asking a question about the anti bleed back valve and what specifically the 502 spec oil plays in the valve's ability to keep oil in the adjuster.

I think if you believe it will fix itself with a different grade oil, be prepared for your wishes not coming true. I would chalk this one up to engine age most likely.

I did not "believe" it would fix itself. What I mistakenly believed is that someone might actually answer the question I asked which was what is there about the 502 spec oil that would inhibit the valve from allowing it to drain oil from the cam tensioners.

Instead, I get "experts" telling me the plastic wears down / makes chain rattle. DUH! After I clarify my specific question for those with trouble reading English, I get a snarky remark, "If I believe it will fix itself, be prepared for wishes not coming true. Ironically "age" is the correct assumption. (not age of the car, but my age). I'm old enough to remember when people actually addressed the question and not comment for the sake of commenting or offering negative remarks.

If this is your fourth A8 then u should know what type of oil to use. The problem is there know either because of oil or because of age. The only way to fix it properly is to rebuild the cam chain guides tensioner and chain. That should solve the problem for a little while. Good luck.

I m positive that either oil 502 spec or Mobile 1 oil will not stay up in the valve train, it will go in the pan once shut off. I think u should find a new mechanic. He is giving you strange info. Once the car is started its quicker to go up through the passages and coat the chain and everything else so it quiets down almost instantly. Your worring needlessly keep driving until it gets really bad or start seeing plastic pieces. Or just get it rebuilt it will be quiet for a while. Everyone has this issue with the 4.2 engine not just you. I've always the right oil and it still makes noise when I start it.

Mr "Older", "junior member": What "mechanic" are you referring to that gave me strange info? I don't remember saying anything about any mechanic making any suggestion or giving me "strange information"

Now for anyone who actually knows the difference and can articulate an intelligent answer as opposed to conjecture / invention of information from a phantom mechanic:

What properties does Mobile One 502 spec have that regular Mobile One (non 501) does not have?

Regarding pre 2004 A8's and "knowing what oil to use" I found this: NOTE: Many pre 2004 Audi owner's manuals did not list the actual Audi oil spec (e.g. VW 502 00). Older manuals many only list the SAE (Society of American Engineers), API (American Petroleum Institute), and ACEA (European Automobile Manufacturers Association) specs

One of my A8s is a 1998 with 175,000 miles, driven very little. From 2002 when purchased with 60K miles only conventional, 5-W-30 oil was used and it never exhibited a cam tensioner noise on start up, regardless of sitting over night or over five nights in below freezing conditions or in in summer with temps 80-90 degree range.

The previous owner of my current 2006 did use 502 spec oil. It made no noise when I purchased with 125,000 miles through the first 4-5 months. A few changes in those 4-5 months Mobile One 5-W- 30 (not 502) was used and it began to make noise. After reading about the bleed back valve, I switched to 0-W40, 502 spec.

Now, I'm trying to understand what connection 502 oil has on the operation of the bleed back valve. Please only comment if you can address this question. If you want to comment with disparaging remarks, go start your own thread.

I can't say I want to help, but I will reply, you really don't need to have your tone for people to help. It's like you woke up on the wrong side of the bed and are taking it out on us.

The spec of oil generally has to do with the additives that the oil producer puts in it. I.E. different amounts of Magnesium, Calcium, Barium, Phosphorous, Zinc, Molybdenum and Boron. These additives, in the correct concentration, help to keep the engine running a long time. The viscosity is something different, but regardless of what spec the oil meets, the viscosity grade is what it is (or what it should be based on the spec).

Based on this, having an oil that meets the Audi 502 spec for the engine, is most likely not going to allow oil not to drain back from a tensioner device. Most likely that device has failed and requires replacement. However, if the correct spec of oil was used 100% of the life of the engine, there is a chance that it could have a longer life as compared to not using 502 spec oil.

Maybe not oil related
 

I have always used “European 0-w40” in mine. But I think modern oil is so good it is an obsolete spec.
Currently using European refined Castrol.. All for last 6 changes was West German. Will run out soon and use Belgium.
I doubt there is an anti-drainback additive.