Possible oil anti drainback issue

[terbogoat]

The patient is a 2004 A8 D3 with the 4.2 BFM engine, 247k miles.

At the last regular OCI I replaced the Castrol Edge 5w40 Euro for Mobil1 0w40 Euro. I swapped the Mann filter for a Wix, filling the oil to exactly the upper limit on the dipstick... and now the engine exhibits what seems to be a drainback situation.

When the engine is started after an overnight sit, it makes all manner of horrible sounds, much louder and longer than the infamous brief timing chain rattle I normally hear. I'm able to avoid this by cranking for several seconds with the injector fuse pulled, then it will start with little to no noise.

Upon shutting the engine off, the oil level rests at the halfway mark. Over the course of several hours/overnight, the level slowly rises to well above the upper mark.

I'm thinking the Wix filter, even though it is a trusted brand, is not playing nice with the anti drainback mechanism. Either that, or the valve is old and brittle and somehow became compromised when the filters were swapped.

I plan to switch back to 5w40/Mann but while I'm waiting on those I thought I would run it past the smart minds here for advice/opinions.

 

[Dr Sheldon]

Wix filter, even though it is a trusted brand,

No they are not !!!

Wix make websites !!

 

[Crasher]

@ Dr Sheldon, WIX are part of MANN+HUMMEL, someone needs to have the cojones and say this, you need to take a look at yourself in the way you treat people, aggressive, dismissive and confrontational; it is unnecessary and pointless.

 

[TTT]

But he says the plain truth. It's just how you deliver the message.

 

[Boki Ar]

@Dr Sheldon, can we make it a little easier, we don't have to shout on the forum.

With all due respect, I would like to ask you.

Please a little nicer turn to the community.

 

[Bruce]

Remember, these are our customers... All deserve respect and honor. No one deserves to be told "You made a pigs ear of that !! Fucked the job !"

In what universe is such considered acceptable behavior?

You have great and deep technical skills @Dr Sheldon. Might you find the means to gain deep proficient skills in communicating kindly the knowledge you possess so that others might learn? That would leave a legacy all could applaud.

 

[Uwe]

I plan to switch back to 5w40/Mann but while I'm waiting on those I thought I would run it past the smart minds here for advice/opinions.

I would change one thing at a time so that you know which thing caused the issue.

I would start with the oil filter because it's easier than draining and refilling the oil. WIX in indeed a reputable brand, but whether it's right for your A8 is another question. If the proper Mann filter doesn't solve this, then go back to 5W40 oil.

-Uwe-

 

[Eric]

I haven't been able to find pictures of inside the oil housing for the 4.2, but if it's anything like the 3.0T, the drainback mechanism is extremely sensitive to the filter's OAL. The filter is supposed to push at one end of a springy blade, to prevent the other end from pushing on the anti-drainback grommet. If your filter is too short even by millimeters, it will have the same effect as no filter at all and the oil will drain back. The grommet itself can also become an issue with age. Here's the spring and old/new grommets on my 3.0T after 10 yrs and 70k miles. AFAICT the drainback system was still working correctly.

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[Crasher]

I certainly wouldn’t be using a 0w/40 in that, 5W/30 for me.

 

[terbogoat]

Thanks a million for the responses.

Uve, I'll take your advice and start with the filter... my hunch is that is more likely the issue than the oil.

Eric, I was not aware that slight filter length variations could cause problems... perhaps I can compare the two filters. Were the guts fairly easy to remove? I could not find it in The Bentley and a casual internet search did not reveal a parts source.

Crasher, you are correct. According to my owner manual, factory fill was 0w30 and it goes on to say that 5w30 or 5w40 are suitable alternatives if 0w30 is not available. This engine has some miles under its belt and is consuming more oil than in the past so perhaps 40 is appropriate.

Regarding post #2, it's cool... no offense was taken.

 

[Uwe]

This engine has some miles under its belt

247k miles.

-Uwe-

 

[terbogoat]

It was the filter. The bottom of the Wix filter has a soft felt-like sealing surface which appears to be smooshed in by spring tension. By comparison, the Mann has nice solid flat bottom.

The cold start clatter has vanished; only a very brief timing chain rattle remains and even that may be lighter and of shorter duration than in the past.

A look back at the DIY service records reveals that I have used Wix in the past without issue. Perhaps this one made it past Quality Assurance.

 

[Crasher]

I have no experience of WIX and if we don't use genuine then it is always MANN.

 

[terbogoat]

I was wrong. Oil is still draining back to the sump with the Mann filter installed.

I also had a flawed understanding of how the filter in its installed position holds the anti drain back valve closed. I thought the bottom of the filter is what exerted pressure but it is obviously the top that performs that function.

The little dome-like part in the photos aligns with a small centering hole in the top of the filter, depressing a plunger type affair against spring pressure. I think there may be an o-ring on the other end of that plunger that is no longer sealing properly.

I haven't been able to learn how to remove the center cage assembly for inspection, or if it even can be removed. The Bentley offers no help.

By the way, what I thought was a Wix filter was actually a Hengst in a Wix box.