Oil anti drain back failure
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AudiWorld Junior Member
Joined: Dec 2014
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Oil anti drain back failure
The application is '04 A8 with the BFM engine, 240k miles... you know, the one with the oil filter housing conveniently tucked down under the air box.
I believe the anti drain back mechanism is not working. Baseline oil level is checked at 15 minutes post shut down, then the level slowly rises on the dipstick for the next day or so.
Also, the timing chain now emits an unhealthy sounding rattle upon cold startup for a good 3 seconds (previously only about 1/2 second).
This problem came about after the last oil/filter change. I thought it might be because I switched from a Mann to a Wix filter. So... I replaced the Wix with another Mann. That did not help.
I've been unable to find a parts diagram for the filter housing assembly but there must be an o-ring affair at the bottom of the center tube.
My question is: Can this center tube be removed in order to renew the seal(s)? The tube seems loose/floppy within the housing, has always been that way so it is assumed that is normal. I hesitate to pull/twist on it for fear of breaking something.
I believe the anti drain back mechanism is not working. Baseline oil level is checked at 15 minutes post shut down, then the level slowly rises on the dipstick for the next day or so.
Also, the timing chain now emits an unhealthy sounding rattle upon cold startup for a good 3 seconds (previously only about 1/2 second).
This problem came about after the last oil/filter change. I thought it might be because I switched from a Mann to a Wix filter. So... I replaced the Wix with another Mann. That did not help.
I've been unable to find a parts diagram for the filter housing assembly but there must be an o-ring affair at the bottom of the center tube.
My question is: Can this center tube be removed in order to renew the seal(s)? The tube seems loose/floppy within the housing, has always been that way so it is assumed that is normal. I hesitate to pull/twist on it for fear of breaking something.
Thread Starter
AudiWorld Junior Member
Joined: Dec 2014
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Thanks for the reply.
I failed to mention that I did replace the check valves since I had the intake manifold off anyway to access a coolant leak. That did not improve the brief timing chain noise the engine was experiencing at the time. It was not terribly objectionable and Audi regards it as "normal" so I lived with it. That is likely tensioner leak-down and it appears engine removal is required to correct it, a task I'm not heartily interested in performing.
Again, the current issue popped up after the oil and filter change which makes me think I inadvertently messed something up in the filter housing.
The oil level rises about 1/4" on the dipstick overnight. That seems like a fairly substantial volume of oil which reinforces my theory that the oil filter housing is draining into the sump rather than any oil contained in the heads.
I failed to mention that I did replace the check valves since I had the intake manifold off anyway to access a coolant leak. That did not improve the brief timing chain noise the engine was experiencing at the time. It was not terribly objectionable and Audi regards it as "normal" so I lived with it. That is likely tensioner leak-down and it appears engine removal is required to correct it, a task I'm not heartily interested in performing.
Again, the current issue popped up after the oil and filter change which makes me think I inadvertently messed something up in the filter housing.
The oil level rises about 1/4" on the dipstick overnight. That seems like a fairly substantial volume of oil which reinforces my theory that the oil filter housing is draining into the sump rather than any oil contained in the heads.
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I haven't seen a lot of information about the oil filter housing and startup pressure. There this post where someone hooked up an oil pressure pre-charge kit to increase oil pressure. It connected to the oil filter housing. Your point about it happening after an oil change is not isolated; I have seen other threads that explain similar behaviors. Other folks say 0w40 in older engines may be too thin and 5w30 is better for the pressure situation. Tensioners are a thing but going back to your oil change being the key point, you have more troubleshooting to do.
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From: Espain
I haven't seen a lot of information about the oil filter housing and startup pressure. There this post where someone hooked up an oil pressure pre-charge kit to increase oil pressure. It connected to the oil filter housing. Your point about it happening after an oil change is not isolated; I have seen other threads that explain similar behaviors. Other folks say 0w40 in older engines may be too thin and 5w30 is better for the pressure situation. Tensioners are a thing but going back to your oil change being the key point, you have more troubleshooting to do.
Thread Starter
AudiWorld Junior Member
Joined: Dec 2014
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I've researched the possibility of installing an oil pressure accumulator but I didn't see one specifically for a D3 until I looked at the link you provided, thanks. I may consider doing that if a solution is not found.
I experimented with various grades of oil and noted no difference in the issue.
What I will do is remove the filter housing drain plug a couple of days after shut down to see how much comes out. If little or none drains out it would at least confirm where the problem lies.
I experimented with various grades of oil and noted no difference in the issue.
What I will do is remove the filter housing drain plug a couple of days after shut down to see how much comes out. If little or none drains out it would at least confirm where the problem lies.
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Thread Starter
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Thanks, that is how I understand it as well.
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From: Chicago
No, it just means it has lower viscosity (ie thinner) when cold. That doesn’t necessarily equate to better lubrication as it also means it can more easily leak out of places where it shouldn’t, so may not be fully pressurizing things. Such as bearings, hydraulic lifters, hydraulic tensioners, check valves, etc etc. This is much more prevalent on higher mileage engines with greater tolerances due to wear. 0W-40 is too thin unless you’re dailying it in Canadian winters. 5W-40 is generally a more suitable approved spec that will very likely improve your situation.
Last edited by dvs_dave; Jun 17, 2026 at 10:13 PM.
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From: Central Ohio
No, it just means it has lower viscosity (ie thinner) when cold. That doesn’t necessarily equate to better lubrication as it also means it can more easily leak out of places where it shouldn’t, so may not be fully pressurizing things. Such as bearings, hydraulic lifters, hydraulic tensioners, check valves, etc etc. This is much more prevalent on higher mileage engines with greater tolerances due to wear. 0W-40 is too thin unless you’re dailying it in Canadian winters. 5W-40 is generally a more suitable approved spec that will very likely improve your situation.