cello

Nice info. Quite clear there is oil infused 'blow by' expected. The question then is how well does the OEM "oil mist separator" work ? The better, the less need to clean the heads; the worse.. well the worse for Porsche from a warranty perspective..

nyca

http://www.mahle.com/C125705E004FDAF...6LGAW417WEBBEN
http://www.mahle.com/C125705E004FDAF...6LGB3329WEBBEN

ADias

It's something like this that seems to exist in the 997.2 DFI as shown in the PAG tech paper referred above (pgs 19-20). PAG may have learned from the Cayenne experience and the 997.2 reaps the benefit.

axhoaxho

Checkout these two interesting videos to show how Porsche DFI engines work.

Regards,



997.2 DFI
http://www.youtube.com/watch?v=hZgXqSj6Ef8

Cayenne DFI
http://www.youtube.com/watch?v=NyTP5LzduyM

zedcat

Very interesting thread although I don't own a DFI engine. So perhaps the best all around offering from Porsche is the Cayman 2.9l 9A1 engine without DFI?

javocat

My 2000 996, 3.4 liter engine, had an oil-gas separator. I know because it began making a loud noise, the dealer replaced it at a cost of $1,200, and then I made a loud noise. So I would guess that Porsche understands the issue with recycled crankcase vapors and dealt with it on the new DFI engines. Or at least I hope so because I now own a 2009 C2.

Clay

+1


Thats what I would do and have done on my daily driver VW TDi.
The TDi's (and other modern diesels) have a problem with the intake manifolds clogging up with gunk because of the PCV and EGR.

The engine oil vapors and exhaust gasses sent to the intake manifold combined to make a lovely sticky sooty mess that chokes the engine after 50-75,000 miles of use.


Different engine, but same principal.

I wonder if the 997.2 engine will throw a code if the PCV is disconnected?

IB Adrian

EGR/PCV on a diesel is a little different than a gas engine.

I have worked quite extensively on Ford's 6.0l Powerstroke diesel, which would probably be the poorest Diesel engine for reliability in this department in recent memory (although some of VAG's diesels aren't too far behind...)
The issues with diesels is directly associated with lack of an appropriate heat cycle and diesel fuels lack of "vaporization" at these temps.

In this instance, if it is occuring, I don't think it will be from the EGR, the temperatures of the exhaust gases should eliminate carbon/sludge buildup, and fuel that hasn't combusted should be appropriately vaporized.
The only possibility that I can think of is that is that the engine blow-by is picking up sump oil, and depositing it on your intake.
I feel the trainspotters are correct in identifying that it would most likely be washed away by having fuel injected into your intake runners, but doing that doesn't fix the crux of the problem, it shouldn't have occurred in the first place!!!
(even if injecting fuel into your intake runners "fixes" having sludge build up around your intake valve, it will not fix oil getting into your intake)
Nor would the fault of this problem (I imagine, unless there is a different PCV design) be specific just to DFI vehicles, the resultant effects (sludge on intake valve), yes.

My rather amateur diagnosis leads me to believe that there is potentially a couple of things at fault:
1. Excessive crankcase pressures/intake vaccum allowing oil to be forced into the intake - much more likely in a turbo'd/supercharged car.
2. Faulty PCV screen/oil seperator (whatever system Porsche use)


At the end of the day, I wouldn't be too worried, I would just seafoam my engine every 10,000 miles and it should be fine.

OCBen

Not a bad diagnosis, Adrian. But I wouldn't say you're an amateur here, based on your experience in this field.

wwest

The DEFINITIVE answer(s)...

12:1 compression ratio with DFI, higher compression results in more blow-by.

Notice the complaints about higher oil consumption for new, non-broken-in engines...?

Higher DFI compression over "normal", historical normal, results in more blow-by during the compression stroke. Rings must more fully seat before oil consumption declines.

PCV passes the crankcase blow-by oil "mist" to the intake, some of the "mist" deposits on HOT intake valve backside and congeals there. Part of the mist enters the cylinder along with the "air" charge, no fuel yet for the mist to intermix/atomize with, so the mist simple deposits on the rising piston head.

Increased compression with DFI requires improved pistion/ring/cylinder wall sealing or else you end up with congealed oil deposits on the intake valves and soot on the tail pipe.

Porsche says oil consumption should decline substantionally once the engine is fully broken in, 3000, 4000 miles, my assumption is that means once the rings are more thoroughly seated.

Fahrer

I am not buying the higher compression ratio as the culprit for higher oil consumption. I had a VW Passat TDI in Germany with, of course, a higher compression ratio than gasoline DFI engines. After initial break in the car used very little oil. And, I drove that car for almost 100,000 kilometers ( 60,000 miles). A lot of that driving was flat out at 125 mph ( not kph) and oil consumption was minimal.

mdrums

I do not by the high compression ratio either...I believe it has to do with the low friction rings, the piston oil cooling on this new engine and 0w-40 oil.

ADias

I started this thread and I think that it has ran its course and I am closing it.