987c

I changed the air filter tonight and it was pretty dirty and had a small amount of oil in the bottom of the air filter housing and the filter looked to maybe have gotten some oil in it over time. Could this be the air oil separator going out? Or maybe from when the oil was changed last week. If it was overfilled could it cause this? It doesn't smoke on startup, or at all for that matter. It runs absolutely perfect and never had a check engine light. It idles great and doesn't hunt at all either. 70k miles. Any ideas?

Macster

That would have to be some horrific AOS failure to oil the filter air box and even the filter element.

If it were from the AOS I think you'd have more sign than just a bit of oil in the filter box and on the element.

As an aside my Boxster went through 2 AOS's and neither time did the air filter box or filter element get so much as a drop of oil on them. The only thing upstream of the where the AOS connects to the intake manifold that had any oil was the TB and its butterfly valve. Upstream of that the intake tube was dry and clean.

How to explain the oil in the filter box and on the filter?

If the oil was changed concurrent with the air filter that could explain it. But I am not familiar with the engine layout of that MY Cayman to know if that's a viable explanation.

987c

well thanks for the reply. I agree it doesn't make sense either. I should go check it again since I replaced it and see what it looks like. I bought the car from the original owner and he told me the last service had a gasket replacement, but he didn't remember what it was. I'm thinking most likely it was a leaking manifold intake gasket. Could that drip down to the air filter housing?

987c

Just checked the air filter again Macster and it was very clean, still looks new and no sign of oil. I'm guessing the issue was fixed, whatever it was, but the air filter was forgotten. Either way I'm pleased to see everything looks good.

Macster

If the intake manifold was removed to address a gasket leak that could account for the spot or stain you found. The intake's inner walls downstream of where the AOS hose connects is almost always wet with oil, so the techs tell me, and the intake manifold being removed and moved around probably stored at an odd angle could have had some oil run down into the intake air box and even drip a drop onto the air filter element.

987c

I'd say that's what happened.
You can see the small amount of oil in the pic.

DogInBlack

There is next to zero chance of oil getting into the airbox from the Air/Oil separator or intake at all. I would be a dollar to a doughnut that it came in from the outside, hence, your air filter worked exactly as it should.