Replaced OAS O-Rings, Still Oil in Intake [86-944]

exitwound · exitwound's Garage

We replaced the OAS (oil air separator) O-rings a few months ago to stop a pesky leak with success. There was no new oil to speak of outside the engine. However, investigation a starter issue today, I came across oil in the intake, and it looks like a pretty good bit of it. The milkshake is only in color (as it's probably just water condensation mixing with the oil). The oil is still runny and thin despite its thick appearance in these images.

What are the main causes of oil in the intake that I should look for? There are no leaks around the OAS from the outside of the engine.

exitwound · exitwound's Garage

Bump on this one.

No ideas?

blown 944 · 08-30-2007, 01:59 PM

Excessive blowby coming through the AOS.

I would try to put a separate catch can on for a bit to see how much oil is coming through the AOS. If it is managable leave as is if it is really dumping oil out you may need to to look at some new rings or guides.

I personally don't like the AOS design it seems to be able to pull too much vacuum through it and scavenge excessive oil. I have ran mine for a while w/o the AOS being drawn into the intake tract and it seems good. I did experience a little ooil in the catch can when I ran high boost on the motor but not out of the ordinary

nynor · 08-30-2007, 02:02 PM

what oil are you running? any additives?

exitwound · exitwound's Garage

Standard 10W-30 oil (I believe) with no additives. We did a pressure test a few months back and the results were in the green (GOOD on the pressure tester). Rings are older and not new. That amount of oil has collected since no earlier than June which is when we first discovered the OAS leak and when we changed the O-rings there.

nynor · 08-30-2007, 02:17 PM

where i am going with this is foaming. i am wondering if your oil is foaming or otherwise becoming aerosolized.

onZedge · 08-30-2007, 02:49 PM

I'm with Sid, excessive blowby. The oil cap has a big O-ring. Did you try replacing that? There is also an O-ring where the dipstick tube plugs into the block. Did you try replacing that? Does the dipstick seat firmly? These are some other ways air can get into the crankcase. Of course, there is always the piston rings, but let's not go there yet...

fast924S · fast924S's Garage

On old cars there is usually some oil in the intake, but that much oil in that amount of time is alot, Is your oil level correct??? Also do you track the car??? I never really like the idea of venting the crank case into the intake, That means your sucking in dirty hot air, But its for emissions, I would do a compression check and a leakdown check, Make sure your oil level is correct. Then if it still happens, I would just go buy a cath can kit from lindsey racing and be done with it

onZedge · 08-30-2007, 06:44 PM

Actually, the crankcase vapor system on these cars is not a positive ventilation system like most cars. This system is designed to simply pull a slight vacuum on the crankcase to give the expanding vapors somewhere to go as the oil heats up. You will get excessive blowby in the j-boot if the crankcase system is not sealed, hence my mentioning the o-rings for the cap and dipstick.