belgiumbarry

on the '82 928S rally car build i have excessive oil out of the tower... sandwich plate under the tower and catch tank ... still it blows the oil out. 10 dyno runs was good for 1 L oil under the car ....

what can be the reason ?

Mrmerlin

sounds like excessive blowby,
might be time for fresh rings

belgiumbarry

yeah... i was afraid of that .
On the other hand , compression test was perfect .. can that with worn rings ?

hacker-pschorr

Detonation can cause blow-by, check your tune and don't always trust knock sensors.

GregBBRD

That's not as simple as it seems like it should be....a chronic "928 problem", from the first model to the last.

All 928's suffer from the same basic design issue...rpm's put a a lot of oil into suspension and can whip up the oil in the oil pan. The crankcase pressure goes up, effectively blocking the return paths from the cylinder heads. Oil is then held in suspension on the entire top end of the engine. When the crankcase pressure builds to a high enough point, there will be a giant "burp" and the oil gets ejected.
The longer the engine is held at high rpms, the worse the problem gets.

Fortunately, the two valve engines can't "store" as much oil in the heads as the 4 valve engines, so "uncovering" the oil pick-up (sucking air results in almost instant rod bearing damage) is much more rare.
On the other hand, if you study how the two valve engines "vent" the heads, it's quickly obvious that.........they don't.

The first (and most basic thing) to pay attention to is the oil you are running. Steal an electric kitchen mixer (or a hand whisk), heat the oil up, and try to aerate the oil. Some oils are better than others at not aerating.

Most of the "baffles" made to go under the filler neck make the problem worse. The baffle must act like an oil separator when oil in suspension hits it, not block the air/oil once it becomes overwhelmed.
I'm not sure if you have the early oil pan pick-up assembly, in your engine, or not. This design really helps to keep the oil in the oil pan, due to the screen and the cloverleaf pick-up and is definitely a step in the right direction.
Moving the oil away from the crankshaft (pan and pick-up spacer) helps, in conjunction with simple windage trays (when the early oil pick-up assembly is not used.....when the early oil pan pick-up is used, rear windage trays and pan spacer helps.)

buccicone

No Knock Sensors on 1982

belgiumbarry

i did some tests...

down pipe from oil tower in a oil can and clear vertical plastic hose on the pan tube : oil sure doesn't come higher then the metal tube itself . ( test for crankcase pressure )
And again dripping oil from the catch tank...

Then i let the hose bend from the oil tower vent direct in a cola bottle in the V .... no oil mist ! If it works out that way it is as the long hoses, catch tank etc... give some back pressure and that makes it possible to carry oil mist . Will this test further and ,if so , see for a proper solution. Meanwhile i'm lucky , we have enough empty cola bottles

Ad0911

This leads eventually to a home made dry sump system. Another new development for the 928! All those 911-s were right all the time!

Strosek Ultra

BMW Cyclone Oil Separator part no. 11151705237. Two is good for a V8.
Price is good.
Åke

olmann

I have two of those plumbed in on my SC setup and they work well. One for the valve covers and one for the oil filler neck.

Bulvot

FYI - I just pulled a few ounces of water out of my oil separator that I use on my oil breather system for my turbo charged 928. I collected none in the warm weather, so it was definitely a function of driving it in the cold. If you are plumbing the condensate back into the sump, you're providing no path for water condensate to escape the oiling system. Just something to consider.

Petza914

My AOS has a compartment in the back to keep it warm. It's plumbed for the heat exchanger fluid (windshield washer fluid) that's used for the supercharger setup to pass through that compartment as an AOS heater so you don't have the coagulated oil issue that happens when driving in cold weather with most AOS setups. It's also not particularly cold where I live and I don't usually drive the Porsches if it's below 40 as they all have summer performance tires on them. Most modern PCV systems are closed and vent air from the system back to the intake for burning off the condensate that evaporates away when the oil gets up to temperature anyway. Mine vents it to atmosphere when it becomes vapor. I have no foaming or other evidence of condensate accumulating in the oiling system, likely because of the AOS being heated.

It's one of the main reasons I chose this particular AOS to use since I was plumbing it back to the sump.

Bulvot

The heat helps it flow, but doesn't stop water from condensing into your oil. But, since you don't drive it in cold weather it may never become an issue for you. If you do drive it in cold weather, your heated AOS will not prevent water condensate from getting into your oil.

Petza914

Water condensate gets into all oil, but then evaporates out during longer drives when the oil is up to full temperature. That car also has the cloverleaf pickup in the oil pan and windage screen so no frothing happening in the sump.

Bulvot

Only if there is a place for the water to leave the system. An AOS condenses the water, and it doesn't leave the system. Even if it's heated. Not a huge problem in the summer, but in the winter it builds up significantly. Take it or leave it. Those are the facts.