MP4.2+6.0

Nope, that really is a non-starter, both functionally and component wise. The PCV valve is dealing with oil blow by from the crankcase. That means unburned hydrocarbons, and oily ones at that. You want to dump those into the combustion chamber to burn off, not after it to then pollute or need to be cleaned up further. PCV valves and venting back to the intake were probably THE first smog thing introduced, mid 1960's if I have it about right. Pre-1975 there was no catalytic converter to burn off anything post combustion chamber either. Further, if you dump it post combustion chamber, it is right in front of the forward O2 sensors, and then the cats. You really don't want to dump anything oily there, especially continuously, and you don't want cats working overtime cleaning up stuff. Would shorten longevity of both. They can't clean up anything until they light off (reach op. temp) either, and most remaining gas vehicle pollution is either vapor emissions or pre-light off of the cat. Hence richening the mixture with an air pump, heated O2's, cats moved close in now to the manifold or built into it, and the like.

BTW further often overlooked in this is the water that also builds up a lot on cold start up that comes through the PCV system. Throw that into a mix with oil and you have classic emulsified crap. No intake valve washing on a FSI motor of course means no solvent cleaning either. A better or worse designed PCV system that deals with both oil AND water can either help or hurt here. One of the big reasons vehicles with a lot of cold starts, short drive cycles and incomplete warm up may be more prone to the fouling issues.

KnappAttack

Emissions. They need to burn it up in the combustion process to keep the emissions clean and in check, plus oil in the cat would plug it up also along with the o2 sensor, and in a turbo engine, the pressure would be much higher than the crankcase pressure if you try and do it pre-turbo.

Honestly, we used to run a Moroso crankcase evacuation system into the headers, with the headers putting the pull the crankcase plumbing using a venturi effect. We did that prior to vacuum pumps way back in the day.

Ravill

Yes, I know all these things. I suppose I was asking a rhetorical question.

There must be a better way.

KnappAttack

There sure is! Go back to port injection where the fuel keeps the intake clean!

MP4.2+6.0

If you track what Audi is doing with the 2.0T, a guess is they are likely to do a port and direct combo going forward. The first iteration on the 2.0T put a fifth injector back into the intake manifold. That washes the valves and also is used for some added power. Found in current 2.0T's being shipped, like the 2014 and forward Q5 that picked up a few more HP with it. There is now another design that has both DI/FSI injectors AND another set of port injectors. Found in the EA888 motor shipped in Euro S3's and TypeR's. Audi says it can get both more power and economy that way, plus obviously it cleans up the fouling issue. A few articles from a while back about that design: http://blog.caranddriver.com/audi-gi...rbo-diesel-v6/ or Volkswagen EA888 four cylinder engine - Volkswagen Golf engine Presumably not D4 4.0T material at this relatively late date--and they already said 450HP on tap for next year. But don't be surprised to see it at or shortly after D5 launch.

ex-quattro PETE

Does anyone have a working link to this file?

All my google results point to non-existing locations, unfortunately.

MP4.2+6.0

Ugh, looks like maybe Audi/VW scrubbed the web again to pull stuff down or something--copyrighted. I searched on it using the document number (SSP 920223) and type: pdf modifier and couldn't find it at all.

For any of the Audi technical documentation, any time I do find it I save a pdf pronto. The links are often fleeting or broken over time.

ex-quattro PETE

Found it:
https://www.audiworld.com/forums/att...self-study.pdf

ex-quattro PETE

There are two aspects of engine oil that may have some impact on the forming of deposits on intake valves. One is Noack volatility, which describes evaporative loss. The lower the volatility of an oil, the less it will evaporate when heated, hence less of it should find its way to the valves, at least in theory.

The other is SA (sulfated ash). Some additive producers (mainly Lubrizol) are claiming that low SAPS oil can help reduce intake deposits: less ash forming additives to cause deposit build-up. These new ashless additives are slowly making their way into the marketplace.

Historically, VAG (and other German makes) would advise against the use of low SAPS oils in their gasoline engines in North America because of the high sulfur content in our gasoline. Sulfur causes faster depletion of the additive base in the oil, which means a low SAPS oil with a weaker add pack has a difficult time making it through the full 10K mile recommended oil change interval. But we are slowly starting to catch up to other western countries and moving to ultra-low-sulfur gasoline here in the States now. Not sure if we are there yet though...

My question is: does the crankcase breather module (coarse and fine oil separation) essentially plays a role of a catch-can that I've seen some DI engine owners install on their cars?

MP4.2+6.0

On the oils, I have been looking into this for a while. Goes all the way back to when I got D3 W12 and found Euro spec was 503 in 0W30; now folded into 504 IIRC. My 2006 W12 had a fine oil separator--one for each side of motor. Probably about when it debuted. At time I didn't really appreciate what it was doing, but did realize over time it also subsumed the whole PCV system of prior motors. Also found from W12 intake pulls (typical best way to do W12 spark plugs and other maintenance and way easier than most motors to pull), the valves were still pristine even at last pull about 120K miles.

Actually, the tip off for D4/newer motors was when I found buried in the EPA mileage test source data they have on the web that Audi has been shipping the 4.0T into the states for at least the last several years with a 504/507 oil, not the typical 502 oil. They run the 4.0T with 5W30 fill. The 502 oil in 5W40 is what is still going into the 2.0T (and 3.0T IIRC). My guess is their motivation may have been to squeeze out a bit better 4.0T MPG's for that test.

Surprisingly when I looked in my 2015 D4 owner's manual, they also now say specific to the D4 that you can use 502 or 504. Thus the "old" 502 only recommendation is gone in the USA owner's manual. But along lines you mention it is the continuing Audi internet echo that will probably be around for years still. On my Q5, the 2013 manual for mine just talks about 502. But I used a 2016 VIN to pull that manual for Q5, and sure enough it now also references both 502 and 504 just like the D4 manual. Screen shots of the D4 A8/S8 2015 manual page and then the 2016 Q5/SQ5 page below--including Q5 since you have that too and to tie into other common Audi motors.

Next I found CA where I live actually cut over to ultra low sulphur gas formulation some years ago now. The rest of the country was supposed to be there by 1/1/17 from what I found, but since I had my CA answer I moved on without trying to figure out if rest of country did in fact get there. My sense was the answer was yes though.

Net, and especially when I found 504 spec 5W30 was the oil they disclosed to EPA, it cause me in turn to order a bunch of 504 Audi dealer type Castrol Professional from audiusaparts. A little over $7 a bottle, so meaningfully less than any of the similar "ESP" oils found (sparingly) on store shelves. Per quart not even that far off the very common Mobil 1 0W40 502 compliant oil in the 5 quart jugs from Wally World or Amazon. I will be running that in 4.0T going forward when possible, while Q5 will stay at 502 (5W40) given four banger workout. Even better, since it is the Castrol Professional, it has the uV dye marker Audi sometimes looks at for warranty claims apparently in the post TDI crack down on everything era. My guess is Audi dealer fills under AudiCare will still be 502 from their bulk stock of that in Castrol Professional, but at least I will get in into D4 in "tweener" changes in meantime.

And last, yes conceptually the fine oil separator would be doing the same sort of thing but without the catch can kludge and the periodic crap/water draining. As I mentioned, back to D3 experience it is in lieu of what you think of as the PCV system and where a catch can typically ties in IIRC. Bought one for Mini S DI and known fouler but never implemented it before car got totaled.

For other folks with interest BTW, 502 vs. 504 key spec. comparison is below from typical source Lubrizol generator. Folks can see in turn why 504 makes good sense--if the gas formulation is up to snuff and the Audi motor spec includes it.