An oil screen hypothesis.

[kaploww]

I've been looking at the oil screen extensively for quite some time, and had a light bulb moment the other night.

The facts:

The original oil screen that fed the turbochargers had a very fine mesh in it. This mesh filtered down to a micron level that was finer than what the factory oil filter would remove from the oiling system.

The oil lines run vertically out of the valley next to the exhaust manifolds, and next to the turbine housings of the turbochargers.

The oil lines do not have heatshields on them.

The oil lines are fed directly from the oil galley that feeds the cylinder heads, and numerous other solenoids/sensors.

There is a screen in each cylinder head that filters the oil post oil filter as it feeds into the cylinder head.

There is a check valve below the oil screen that feeds the turbochargers to prevent drain back from the oil lines into the cylinder heads.

The software was revised by Audi, and was pushed from the dealerships to add a longer post engine shutdown fan runtime about the same time the revised more porous oil screen was released.

Journal bearing turbochargers have operated on countless other vehicles from the dawn of turbocharger journal bearing technology inception without an oil screen, without damage to the journal bearings of the turbos in some cases millions of miles on diesel trucks without rebuilds with oil that is significantly dirtier than even a neglected 4.0t would be without issue.

The hypothesis based on these facts:


The fine mesh oil screen was not installed to protect the turbos, and the screen clogging resulted from coked oil particles collecting on the screen during oil drain back post engine shutdown. This problem being exacerbated by poor oil maintenance, or incorrect oils used by owners.

There is a screen installed pre cylinder head that is designed to protect the cam bearings, lifters, and cylinder on demand system from contamination.

Think about it.

You shut the engine down after a hard run. You have oil in very thin lines, without a heatshield sitting next to hot exhaust manifolds, and a hot turbine housing on engine shutdown.

Non-synthetic oil can begin to break down at 300F, and cause "coking" carbon buildup, and leave carbon deposits.

You shut the engine down, oil pressure goes to zero, the check valve shuts. The oil begins to sit stagnant in the unheatshielded oil lines in the valley next to these hot components. The oil cannot drain back at a significant rate. The oil begins to cook in the lines.

While the check valve is closed, there will still be a small amount oil that sneaks past, and that oil will continue to drain into the valley the longer the engine is shut down.

The coked oil begins to drain back as well. Without a screen installed directly above the check valve, the particles resulting from coking begin to collect around the check valve, potentially causing it to stick open.

The particles from the coked oil begin to collect in the oil galley that feeds the lifters, the cylinder on demand equipment, and numerous other solenoids\sensors.

I believe that the screen was installed to prevent drain back from the turbochargers, post engine shutdown, from allowing coked oil particles to collect in the oil galley that feeds the turbochargers and all of the top end oil consumers. That's why it was originally a very fine screen with the ability to filter a micron level that was tighter that the OEM filter.

A journal bearing turbo can happily eat quite a big of dirt of significant size prior to it causing damage. The bearing tollerances are fairly loose by comparison to the equipment below the turbochargers. There is a lot of sensitive equipment below the turbo feedline that does not need the introduction of coked oil particles from collecting in them

I believe the extended fan runtime was added to minimize the potential effects of coked oil from collecting against the screen on engine shutdown.

I have only seen significantly clogged screens on cars that ran low quality oil, or were not diligent about their oil changes.

My takeaway.

1) I would run the G revision screen, or no screen at all if you're committed to running high quality oil with religious on time changes.

2) Allow the car to cool down for a bit with a little easy driving prior to shut down.

3) Change your oil religiously

You should avoid the turbocharger oil starvation problem from a clogged screen in its entirety if you follow the three listed steps above.

[qcrazy]

I have heard other similar theories on this and I don't buy it.

For one. The check valve seals tight. And doesn't drain back because the back pressure is so low. When my turbo popped I couldn't get to my car right away so I parked the car in the shop. About 4 months later I had all the parts and pulled it all apart. When I unbolted the feed lines, all the oil poured out all over inside my vee. The lines where still full after ~4 months. I was not expecting that, but when I checked the check valve design it made sense. The valve doesn't leak.

With that in mind, the oil that would drain back on engine shut down is a small amount and would be below the screen. It also wouldn't be coked at the time either.

Even if the check valve seal was bad and the oil drained back. On your theory, the particles would be on the upstream side of the screen, so when you re-start the car the next time all the particles would be blown through your turbos...and not remain on the screen.

There was a mechanic saying is was the check valve a long time ago. If you really think it was the check valve, it would be easier to just pull the check valve and let the oil drain back through right away so it wouldn't coke. This is what that one mechanic was recommending.

When I pulled my screen I was considering pulling my check valve at that time. But when doing more research I saw that the B9 S/RS4 have the check valve and no screen. So I left the check valve. The oil lines in the B9's are in a similar environment to the C7. But on that car Audi pulled the screen and left the check valve. Same thing with the C8. To me, that said the screen is the issue and Audi knows it.

[kaploww]

Check valve removal to prevent coking is possibly an option as well.

I do think the oil cooks inside those lines post shutdown.

Which is why they updated the software to increase airflow in the engine bay post shutdown with a software revision.

It ramps in hard, and extends as oil temps are higher.

[Alabama]

2) Allow the car to cool down for a bit with a little easy driving prior to shut down.

3) Change your oil religiously

Seems like a good recommendation for any high powered turbo car.

The oil lines in the B9's are in a similar environment to the C7. But on that car Audi pulled the screen and left the check valve. Same thing with the C8. To me, that said the screen is the issue and Audi knows it.

I guess we'll see what Audi proposes as the solution for the recall.

Keep up the dialog. We all learn when you knowledgeable folk debate.

[ericw.]

That's quite the hypothesis you came to all by yourself considering you were part of this discussion earlier in March:

The reason the oil screen plugs is because there is a mis-match between the micron rating of the filter and the micron rating of the screen. This is expected, if the filter matched the screen, the screen would be redundant. This is exacerbated by the extremely warm location of the factory screen. But again, the problem is not really the screen itself, it is the lack of serviceability and the lack of a bypass. ...

Kind of like how you claim in other groups to have figured out about the overspin fatigue after I told you it happened, following JHM's diagnosis of my blown turbos. I had to prove it to you with pics.



qcrazy is a legend who actually does the research and posts it. Show some respect.

... Whenever someone talks about how screens haven't been used (somewhat) successfully in previous generations.. There's a variable here that nobody thinks about and it's that this is the very first hot V turbo configuration from Audi. Everything before the 4.0t runs the turbos on the side of the engine.

[Audisthesia]

As ericw has alluded to, these engines cannot simply be compared to "all other turbo engines". These 4.0T are of a fundamentally different design, with countless other variables that us peasants cannot easily account for. It would be awesome if the design engineers explained to us why they put oil screens in these motors, but don't hold your breath.

Curious, the 4.0T in the C8 cars... I read there is no oil screen? Even if so, no one mentions other design changes to the oil system of the engine. Is there simply no other changes (I highly doubt this), or are those posting this information unaware of other changes, or are theu omitting other changes? So many questions... So few answers.

What we know for certain is that Audi has recalled pretty much all 4.0T oil screens, with the distinct exception of MY2018 vehicles(which interesting have Rev G oil screens)... And the repair includes installing Rev G oil screen (unless they came out with Rev H and I missed it).. Food for thought..

All that being said, this forum and discussions and throwing ideas around is how we may ind an acceptable resolution to the oil screen mystery.. Keep it respectful, and debate on!

[Dasquade]

My 50 cent as low educated non mechanic...
I kinda do believe heat and location is one of the main issues. As pointed out, hot V near the end of engine where there is almost no air circulation (even with my a2a setup that opens up the front and valley since it doesnt have the big plastic manifold etc...). During driving heat is okeyish (my data of aftermarket temp sensor at end of valley at the oil lines show +-30-40°C during a long cruise and that is with both manifold covered in heatshield + hot side turbos + dps). Once you stop the car heat builds up quick and high especially with hood closed!! Add the fact the oil circuit stops running and the thin alu pipes (with i wrapped with heat refecting tape).

Anyway, guess it is combo of things (how you drive it, condition of oil, region and ambiant temps, open hood etc...).
My screen was not that bad tbh at 115.000km/7 years, the oil valley did however had decent "burned/carbonish" finish on the metal despite my every second oil change i did an oil flush treadment.

For stock turbos/journal ball turbos i would say no screen is okey since they require lots of oil and arent that picking on friction. For ball bearings i feel more safe with extra external oil filter.

[qcrazy]

Curious, the 4.0T in the C8 cars... I read there is no oil screen? Even if so, no one mentions other design changes to the oil system of the engine. Is there simply no other changes (I highly doubt this), or are those posting this information unaware of other changes, or are theu omitting other changes? So many questions... So few answers.

The C7 RS/S...
C7Screen.JPG
The C7 screen is specifically labeled for the turbos in the SSP. One could say that it is named based on the location, but that would be an atypical name from an engineering standpoint. Typically the name for an ancillary component is based on what equipment it is related to. In my work, if I was using the screen for the check valve, it would be named something like "check valve backflow screen", or something similar. To me, the fact that is is named with the turbos would indicate that it is related to the turbos. Conjecture here for sure. But that would be standard engineering practice.


The C8 RS...
C8 RS6 Oil Filter.JPG
No screen.


The B9 S/RS...
B9S4OilFilterModule.JPG
No screen.

As far as differences, the C8 and B9 have a few obvious differences on the turbo feed compared to the C7. Obviously, screen vs. no screen. But also, the distance from the turbo feed from the oil filter is significant. Both the C8 and B9 feed the turbo's directly off the oil filter housing, compared to much further back on the engine in the C7. I suspect this is more for convenience and cost; a simplification of the oil filter location and reduced machining costs for the oil galleries. The other one that jumps out at me is the oil flow. Both the C8 and B9's are inside-out filters (dirty oil in the inside, clear oil on the outside). The C7 is the opposite of this. In my experience, the C8/B9 oil filter flow (in-out) is more common, but that is just my experience and I am not sure how well that holds up across the industry.

[Alabama]

The other one that jumps out at me is the oil flow. Both the C8 and B9's are inside-out filters (dirty oil in the inside, clear oil on the outside). The C7 is the opposite of this. In my experience, the C8/B9 oil filter flow (in-out) is more common, but that is just my experience and I am not sure how well that holds up across the industry.

For what it's worth, the Mobil website example for the function of an oil filter has the dirty oil entering on the outside to pass through the filter and exit through the center. But how can you trust those C8 and B9 drawings when they don't even use the proper name for the "pressure relief valve"?

[qcrazy]

That is proper. Those are the bypass valves (bypass the filter).

The PRV's are much closer to the pump, near the pan. Typically before the first user (e.g. oil cooler). Totally different function.

[Alabama]

That is proper. Those are the bypass valves (bypass the filter).

The PRV's are much closer to the pump, near the pan. Typically before the first user (e.g. oil cooler). Totally different function.

I misunderstood your comment in a different thread. I thought the terms were interchangeable (interfil.com). An ASE website explanation is more clear (also illustrates dirty oil on outer side, through filter, exiting from center) so I think I've got your point now.

[WhiteDiamond]

The C7 RS/S...
The other one that jumps out at me is the oil flow. Both the C8 and B9's are inside-out filters (dirty oil in the inside, clear oil on the outside). The C7 is the opposite of this. In my experience, the C8/B9 oil filter flow (in-out) is more common, but that is just my experience and I am not sure how well that holds up across the industry.

More surface area for the oil when flowing from outside to inner. I would really like to know why so much of the automotive industry goes opposite and flows from inside out on the filters. Has to be a cost in machining or something, IMO.

[qcrazy]

One of the main advantages of the inside-out is the simplicity of the bypass design. If you look at the C8 and B9 filters above the bypass sits at the end of the filter. Simple.

With outside-in you have to machine the bypass into the base of the filter housing somewhere. On the early C7's they didn't get this bypass set-up right and there is a TSB about them leaking (bypassing).

[kaploww]

The more I think about this, the more I am confident I am correct.

I think the coked oil particulates collect against the screen post engine shutdown.

They are hot.

Rest against the screen while still malleable/slightly gooey.

Cool, and stick in place post engine shutdown as the oil cools.

Over time, this clogs the oil screen.

The particles collect against the screen, and the check valve in turn is protected from the coked oil particulate matter from collecting around and eventually in to the check valve.

As far as this engine being “different”.

That is precisely what I am addressing.

The oil lines are going to be hotter in this engine bay than others due to their proximity to the turbocharger/manifolds/turbine housings.

They are then insulated by all the crap around them, and they just bake on shutdown.

That’s why Audi increased fan run times with a software revision post engine shutdown when the engine oil is hot.

That’s why they went to a more free flowing screen design.

While their initial screen kept the valley immaculate. I’d be willing to bet they decided the trade off between super clean valley and clogged screen was not worth the squeeze.

I also think that check valve is there to protect the top end.

I think it’s there to work like a straw that has been dipped in a soda with a finger over the top of it.

I bet it’s there to prevent oil drain back of the valley that feeds the top end of the engine. Thus allowing minimal time on the next startup for oil flow to reach the lifters, cam bearings etc.

The fact that it traps oil between the turbo lines and the turbos is an added benefit and a designed in feature, as the check valve is also present in the N/A motors.

This would reduce overall top end wear on engine components.

Where as if the check valve wasn’t there, the oil in the top end feed galley would drain straight back to the pan, and there would be a brief period of time on each startup that oil supply was lacking until full pressure built up.

[kaploww]

As far as journal bearing turbos go…

They can eat quite a large amount of particulate matter before they will see any considerable wear.

Coked oil particulate matter tends to be very fine.

In aviation, if oil temps got above 120C or 250F(ish) we kept an eye on them, as coking would begin to occur, and there was a serious problem with our oil coolers if that ever happened. (Highly unlikely, our oil coolers were bigger than most automotive radiators, and we had a kinda big fan blowing on them. Haha.

250F or 120C is when problems start to occur with oil breakdown.

At 300F… oil breakdown / coking is 100% occurring.

[John@DEADBEEF_DynoSp]

Another data point. I recently sold my S8 and it had only 44000 miles. It was boosting fine when sold, 9 days later the new owner contacts to say the idle became rough yesterday and then a scope shows damaged compressors. The intake filters had been changed once and were Audi original parts so unlikely FOD, oil screen not out yet. I also doubt overspeed as it ran a stage 1 99 RON tune that barely reached 70% WGDC and had a typical boost profile of 1.8 bar peak, dropping to 1.4 bar at gearchange. Private sale and it was driving fine when I sold it, but there is no warranty/recall on these in the UK so I'm paying towards it even though I have no legal duty to do so as I feel bad for the new owner.

The car was driven hard for a few days in 2019 developing stage 1 tunes and carefully cooled if hot, usually just with normal driving the last few miles wouldn't see any boost, but the oil temperatures on most journeys it has had in the last 6 years the oil temperatures have usually exceeded 70C during each trip but rarely gone over 102C and never that I recall indicated over 106C - I live in a cool climate and the roads are narrow and twisting, you just can't go that fast and get it that hot easily. Of course that is a sampled temperature not a peak. When I commuted it in 2014/2015 I occasionally had a short burst of fun, but literally 99% of the time it was absolutely babied. It was always oil changed at the dealer with whatever VAG approved oil they use.

So this would be one of the last cars I would expect to have a blocked oil screen from hot oil side effects.

[gk1]

Another data point. I recently sold my S8 and it had only 44000 miles. It was boosting fine when sold, 9 days later the new owner contacts to say the idle became rough yesterday and then a scope shows damaged compressors. The intake filters had been changed once and were Audi original parts so unlikely FOD, oil screen not out yet. I also doubt overspeed as it ran a stage 1 99 RON tune that barely reached 70% WGDC and had a typical boost profile of 1.8 bar peak, dropping to 1.4 bar at gearchange. Private sale and it was driving fine when I sold it, but there is no warranty/recall on these in the UK so I'm paying towards it even though I have no legal duty to do so as I feel bad for the new owner.

The car was driven hard for a few days in 2019 developing stage 1 tunes and carefully cooled if hot, usually just with normal driving the last few miles wouldn't see any boost, but the oil temperatures on most journeys it has had in the last 6 years the oil temperatures have usually exceeded 70C during each trip but rarely gone over 102C and never that I recall indicated over 106C - I live in a cool climate and the roads are narrow and twisting, you just can't go that fast and get it that hot easily. Of course that is a sampled temperature not a peak. When I commuted it in 2014/2015 I occasionally had a short burst of fun, but literally 99% of the time it was absolutely babied. It was always oil changed at the dealer with whatever VAG approved oil they use.

So this would be one of the last cars I would expect to have a blocked oil screen from hot oil side effects.

Interesting data point, but what was the final outcome?
Is it just assumed it had a blocked screen because the compressors were damaged or was the screen removed and confirmed to be blocked?

What also interests me is you state it rarely got over 102C. I'd think you'd want it to hit at least 100C at sea level every time it was driven to remove moisture from the oil. Might mean nothing, but just interesting.

Also was it VAG OCI too? 10k/1 year. Did it have 4 oil changes in its lifetime or 6 ?

[kaploww]

Additionally the aux oil cooler on the RS cars has a thermostat in it that does not open until 110C

Audi clearly knows oil temp management is an issue on these cars.

Especially as power levels increase as indicated by the addition of an aux oil cooler on the RS cars.

110C is hot. Very hot.

That also indicates that while oil supply from the pan is at 110C.

Consumers of the oil are taking it to temps far hotter than 110C even on a stock RS car.

Then you shutdown the engine.

The hot V literally becomes an oven, and those tiny little lines just bake in there.

The factory engine cover probably exasperates the issue as it has a reflective heat shield on the bottom sending all the radiant heat back towards those tiny little lines.

But… definitely the better option between melting the paint off of your hood over time.

[John@DEADBEEF_DynoSp]

Interesting data point, but what was the final outcome?
Is it just assumed it had a blocked screen because the compressors were damaged or was the screen removed and confirmed to be blocked?

What also interests me is you state it rarely got over 102C. I'd think you'd want it to hit at least 100C at sea level every time it was driven to remove moisture from the oil. Might mean nothing, but just interesting.

Also was it VAG OCI too? 10k/1 year. Did it have 4 oil changes in its lifetime or 6 ?

Assumed, only happened yesterday, we’ll see.

It had 4 oil changes, UK intervals were 18600 miles or 2 years on flexible servicing. Last three were about 7000-8000 miles apart. Did similar on another VAG motor owned from new for 10 years, no oil related problems, sold on original turbo and have had turbo engines for 22 years with no oil related issues before.

It is only recent vehicles I have had that exceed 100C in normal use driven gently. I did not think you needed to reach 100C to actually boil the water off instead of enhanced evap below 100C. If I have to reach 100C on every journey I think I would get a lot of speeding tickets. It would have also left a really narrow range on the R35 GTR where you needed an early oil change if it hit 110C iirc. It never hit it, but was never tracked.

[gk1]

Assumed, only happened yesterday, we’ll see.

It had 4 oil changes, UK intervals were 18600 miles or 2 years on flexible servicing. Last three were about 7000-8000 miles apart. Did similar on another VAG motor owned from new for 10 years, no oil related problems, sold on original turbo and have had turbo engines for 22 years with no oil related issues before.

It is only recent vehicles I have had that exceed 100C in normal use driven gently. I did not think you needed to reach 100C to actually boil the water off instead of enhanced evap below 100C. If I have to reach 100C on every journey I think I would get a lot of speeding tickets. It would have also left a really narrow range on the R35 GTR where you needed an early oil change if it hit 110C iirc. It never hit it, but was never tracked.

Thanks for the responses.

Maybe it is just a difference of US vs. UK driving but it is quite easy for me to hit/exceed 100C on every drive...again it may be right that it is not strictly necessary to hit such temps and there is undoubtedly some issue with the 4.0T in general, just continuing to gather details as others (myself included) have higher mileages than some who have failed. What are we doing (dare I say) "right" to mitigate such issues or is it just blind luck.

[John@DEADBEEF_DynoSp]

Thanks for the responses.

Maybe it is just a difference of US vs. UK driving but it is quite easy for me to hit/exceed 100C on every drive...again it may be right that it is not strictly necessary to hit such temps and there is undoubtedly some issue with the 4.0T in general, just continuing to gather details as others (myself included) have higher mileages than some who have failed. What are we doing (dare I say) "right" to mitigate such issues or is it just blind luck.

Up to now I thought the screen clogging issue would be milder in our cool climate and anecdotally it seemed to be. Will see if it is the screen in this case.

[Alabama]

So this would be one of the last cars I would expect to have a blocked oil screen from hot oil side effects.

Question to you engineering folk from what I'm reading here: Other car manufacturers build turbo V8s without a screen. Audi builds other eight cylinder engines without a screen. How would design engineers even think to install a screen in a brand new engine design? Does a problem exist in other types of engines that they thought might carry over, or was it too much partying at Octoberfest?

[kaploww]

lol @ Oktoberfest.

Nothing is installed without reason, as every single part created or generated for a vehicle increases price and/or eats into their bottom line via R&D time, physically manufacturing the part, and installing it in each vehicle.

Every single step of that process is EXPENSIVE.

They more than likely saw an issue during engine testing, decided the risk of not installing the screen outweighed the potential downsides of installing the screen, and now here we are.

My hypothesis above is what I think they saw during engine testing.

I think they saw fine coked oil particles collecting around the valley/check valve from drain back/gravity in post test tear downs.

The zee Germans were like… Zee oil lines get to hot post engine shutdown, vee vill puts zee screeen in zee valley to katch zee little particles, zen zee particles vill not get to zee check valve. Zat sheise (shit) can go srough zee turbo bearings keine (“without” or “no” in German) problem… and they designed built, and installed a fine mesh screen to prevent particles from collecting in the valley.

[9times]

lol @ Oktoberfest.

Nothing is installed without reason, as every single part created or generated for a vehicle increases price and/or eats into their bottom line via R&D time, physically manufacturing the part, and installing it in each vehicle.

truth

The zee Germans were like… Zee oil lines get to hot post engine shutdown, vee vill puts zee screeen in zee valley to katch zee little particles, zen zee particles vill not get to zee check valve. Zat sheise (shit) can go srough zee turbo bearings keine (“without” or “no” in German) problem… and they designed built, and installed a fine mesh screen to prevent particles from collecting in the valley.

hey, were you in the meeting or something?

[MEnginerdS8]

I've been looking at the oil screen extensively for quite some time, and had a light bulb moment the other night.

The facts:

The original oil screen that fed the turbochargers had a very fine mesh in it. This mesh filtered down to a micron level that was finer than what the factory oil filter would remove from the oiling system.

Kaploww, let me start by saying that while I am new here IÂ’ve enjoyed reading many of your posts and contributions to Audizine as IÂ’ve browsed over the last year before joining.

What is the US mesh equivalent you believe the original oil screen was? Or that someone measured it at.

I removed my oil screen about one year ago and while I did not attempt to measure or benchmark it against known mesh sizes of new material, I would estimate that it was 100 or 150 mesh. 100 mesh screen is used almost universally in commissioning of industrial lube oil systems, including by the GermansÂ… it is quite common to temporarily install screens on every connection to a machine either in the shop or in the field because inevitably there is tubing or piping that has to be fabricated and installed between the lube oil pump, filter, and the machine casing. Likewise the same issue with fabrication debris exists in bearing housings or machine casings, a.k.a. engine blocks and the gallies and cross drilled passages etc must be extensively flushed and blown out to be hopefully free from machining chips.

I Think I have a G screen somewhere in my garage that I chose not to install, in my recollection / impression that was somewhere around 60 or 80 mesh. Again I did not measure that exactly, I am mentally just eyeballing it. 40-60 mesh is typically used for pump strainers, but no respectable millwright or engineer would consider using that for an oil system.

FWIW I proactively pulled out my oil screen at approximately 44,000 miles and it looks pretty darn good… But no regrets in pulling it out. When I had to make the decision whether to reinstall a gutted screen or use the new G screen I came to the speculative conclusion that this was all the fault of some good intentioned German engineer who was solving a problem that wasn’t really there, had ‘over -weighted’ some limited experience where someone had gotten debris into a turbo (such as with assembly, FOD infantile failure), or had gotten overconfident in the fancy varnish resistant oil spec (which is actually pretty darn good but nothing in the real world is perfect). Instead of acknowledging the error, or simply saying it was there as a safety net (which looks bad for their confidence in their German quality), they were stubborn German engineers and simply picked the coarsest screen that they could that looked like it would still do something and that they thought would probably last more like 200,000 miles before plugging. After all, the enthusiast had already figured out that you could run without them…

Here is a reference on US mesh screen sizing:
https://www.industrialspec.com/resou...-micron-sizes/
Notice 100 mesh openings are nominally 150 µm, or ~6 thou. 150 mesh is is ~100 micron, or ~4 thou. Coincidence on the numbers and that they seem to cross at that point, that is why I attached the reference. The efficiency for particle capture at those nominal opening sizes is no more than 50%, and it’s going to vary from manufacturer to manufacture and lot to lot. For the most part though any journal bearing machine will be able to tolerate a particle of that size, even if it is embedding that in the Babbitt rather than allowing that to pass through.

https://www.audizine.com/forum/showt...1#post11996356
Post 15 there shows a nice chart that looks very credible from MANN filter. Looks right to me as industrial lube oil filters are virtually always Spec’d as 10 µm nominal. Some control oil filters, hydraulic systems, and ball bearing oil lube systems will drop that down to ~3 µm absolute (way tighter spec because of being ‘absolute’, or very high efficiency at that rating vs ‘nominal’ aka mediocre at that rating). 10 microns is a 1/2 thou, an order of magnitude tighter than the mesh discussed above.

If you refer back to that chart on US mesh size versus opening size in imperial or SI, you’ll notice that you would have to go past 635 mesh get even close to that particle capture ‘blocking’ performance. The restriction posed by that type of mesh is absurd, there are no pleats or anything to increase the flow area, it might be OK for a ball bearing turbo that would be it… the equivalent orifice size is tiny and so even with a massive pressure drop the flow would be way too low.

Moral of this rambling story, if the screen was really tighter than the oil filter it probably wouldÂ’ve plugged in killed the turbos before the first oil change because the particle count at smaller sizes goes through the roof.

Cheers

[MEnginerdS8]

I did not think you needed to reach 100C to actually boil the water off instead of enhanced evap below 100C.

You definitely donÂ’t need to hit 100 C.

In the 1960s Cooper Bessemer optimize the oil temperature for their fleet of large integral engine compressors, locomotives, and other stationary power units. These 1000-~4000 hp behmoths running 250-350 rpm and easily the size of your living room would run 24/7 and the water from combustion in the blow by would condense in the oil sump if it was not run hot enough. Instead of approaching the problem from the supply side, they worked it backwards from the drain side, or sump temp. Over time they walked the sump temperatures down from approximately 180° F to 165F for the majority of the fleet and 150 F for some of the lower output units. Adjust your viscosity than to what your bearings need, typ ISO 150 is used on large recips and a 150f supply temp to have the drain or some temp upper round 170f.

On separable compressors where are there are no combustion byproducts present unless they have a shared oil system with an engine driver versus a motor drive, sometimes that will be walked down to ISO 100 at ~120f supply temp. There is a higher percentage of free oxygen in those sumps (21% is not purgedÂ…) which changes the exact oil degradation phenomenon.

Another current OEM of gas patch compressors uses 170 F oil supply temperature. That makes it easy to keep the unit cool enough in harsh environments because you have ample deltaT to ambient, but that same OEM will warn you that for every 20°F temperature rise above that, even if your viscosity is OK, your oil life will be cut in half.

That is all just reference points related to driving off moisture though.

In turbomachinery 120-130f supply temperatures are typical with iso 32 or Isot 46 oil and ~150f sump temp being adequate to drive oil moisture (again no combustion byproducts). The oil charges on those units can cost $100,000 and run 10+ years. The differences in the identical units with different initial oil charges is huge, even sometimes differences from the same oil supplier if they have production plants in different regions of the world will result in different performance. So what is the real temperature at which those oils break down? There are instrumented bearings that run continuously for years with pad temps >100C, thus the localized oil temps in the film are far higher.

IÂ’m going to continue this response so that I donÂ’t lose it like the last oneÂ…

[MEnginerdS8]

https://www.kingsbury.com/shoe-temperature-patterns

Here are some sample pad temperatures from Kingsbury, remember that these are intended to run continuously.

You only worry about softening the Babbitt or melting the bearing on those units, not the effect on oil life.

Recip compressors and screw compressors also tell a different story about what temperatures oil really starts to break down at.

We have recips compressors that operate between 400 and 430F discharge temperature, quite a bit hotter than typical. They are oiled lubricated with a once through feed of oil. Yes it is once through which is definitely in its favor, but some people still run into cooking issues on valves. There are conventional mineral oils with the correct additive package that will hold up to that all day. There are synthetic oils that wonÂ’tÂ… that said I still generally agree with the premise that synthetic oils are going to hold up better and are geared more towards high-performance etc. etc.

Oil flooded screw compressors or another great example to look at. I have machines at work that run a process gas with no oxygen in it and we have not changed the oil in 15+ years. The discharge temperature and therefore all the oil coming out of the machine is between 250 and 275F. It is a full synthetic pao with virtually no additive package, because none is needed. To understand that a step further the Adiabitic discharge temperature for those machines can be hundreds and hundreds of degrees Fahrenheit, doing pressure ratios of 10 is fairly common and up to 20 as possible. The cooling oil is providing intercooling, think of it kind of like water meth injection. Instead of there being latent heat of vaporization though, all the excess heat is just absorbed as sensible temperature rise in the liquid oil. If you try to do 20 to 1 compression ratio you actually have to limit yourself to a lower discharge temperature because of the peak temperature reached in the screw on the microscopic vs macroscopic level. Even though the bulk fluid is coming out at 250f, individual pockets of molecules may have seen 500+ f momentarily and been broken down or been polymerized.

OK so how does this relate to AudiÂ’s again? ThereÂ’s not actually a lot of free oxygen in the crank case, or at least thereÂ’s not supposed to be. These oil temperatures are not actually that scary. Now is a 18,000 mile oil change interval appropriate? Probably not especially for those pushing hard, so fully agree with the recommendation mini make for enthusiast to pull in there oil change intervals, I do that myself.

Oil varnish is far far more soluble at high temperatures. It may form at higher temperatures, but it is also more soluble at higher temperatures, and it tends to plate out as temperatures drop. on machinery with known degraded oil there are special additives that can be added just prior to a oil change, but the other key to getting all the bad oil out is that when the machine is shut down you have to isolate the oil cooler, and be prepared to drain everything as hot as possible.

Varnish is going to be attracted to a screen like that no matter what. If you have excessive varnish particles forming in your oil because youÂ’ve used a lower quality oil or pushed the interval too long itÂ’s going to want to come out on that screen. Even if you run a turbo timer or let your vehicle idle down after running hard, drive a few miles easy etc. if youÂ’ve got bad oil in there you can be plugging that screen up even while youÂ’re doing those other behaviors that are supposed to help. IÂ’m not saying that they donÂ’t help, but they help for a different reason, they help prevent the deposits near the turbine bearing, and in the feed lines which could overheat someone on a hot shut down (full or oil and perhaps even worse IF someone wanted to let the oil drain back). In other words those strategies are supposed to help a little bit in limiting the formation of varnish in the first place. Once you have varnish youÂ’re going to run into it in different places throughout the system including near where it was formed such as hot running bearings or other sources of heat, places where the oil temperature drops, example out in your oil cooler, and other places like screens that donÂ’t really need to be thereÂ…

Cheers,

P.S. I donÂ’t mean to come at this like a bull in a china shop, but iÂ’ve worked around a lot of related things for a lot of years, and hopefully some people appreciate the commentary.

Cheers

[MEnginerdS8]

Ok, one more anecdote about oil temperature; completely counter intuitive but sometimes you can extend the machinery and oil life by running the oil at a higher temperature. If a bearing is a bit starved for oil it will tend to run extremely hot in the loaded area, in the film or oil wedge itself and can break down there. Again the primary concern is typically the softening of the bearing Babbitt and its load carrying capability, but you can also start to get into localized varnish issues there. Raising the oil pressure may or may not work because there may be a tendency just to push more oil to other bearings with the extra pressure, possibly create an oil leak or an issue somewhere else, and not really cool off the bearing that needed the help. Another strategy can actually be to raise your oil supply temperature in thin out your oil viscosity. If you were running pressure control you may have the exact same supply pressure, but with the lower viscosity you’ve actually increase the flow to all your bearings and reduced the amount which is just getting recycled by the pressure control valve (assuming a positive displacement pump and constant overall volume of oil supply). With a higher flow of warmer oil you can still potentially extract more heat from the bearing and have the bearing actually run cooler. This can be an overall net benefit to the system, the bearing, and the oil life so long as it is done within reason.

So what does this have to do with Audi’s? I guess not much, just that sometimes there is even more instrumentation available on other larger systems as an analog that can provide additional insight into the way things really play out… the peak oil temps I do not think are the root cause and not even the strongest contributing factor here.

My 0.03….