Air Oil Seperator - Common Issues?

[The Beanster]

My 997.2 TT makes a "hooting" kind of harmonic from the engine area. It is most obvious at idle and when lifting off the brake (coasting from idle). I had the AOS replaced a year ago and thst solved the issue but it's making this sound again. Is it common for the AOS to go bad so quickly? Is this sound a symptom of an AOS that is in any way damaging the cats?

Edited April 26, 2016 by The Beanster

[JFP in PA]

My 997.2 TT makes a "hooting" kind of harmonic from the engine area. It is most obvious at idle and when lifting off the brake (coasting from idle). I had the AOS replaced a year ago and thst solved the issue but it's making this sound again. Is it common for the AOS to go bad so quickly? Is this sound a symptom of an AOS that is in any way damaging the cats?

 

Failures of recently installed, and even right out of the box AOS units is unfortunately an all too common occurrence.  We test every unit we install, and the one on every car that comes into the shop; some seem to last forever, others not so much, and to date we have found no way to separate one from the other.

 

While a bad or failing AOS can inhale more oil than a good unit, the larger concern is having the engine ingest liquid oil and hydro lock.  Long term burning of excessive oil can shorten cat life, but the liquid oil issue is far more critical. 

[The Beanster]

In your experience, how often is hydro locking happening because of a failed AOS?

[JFP in PA]

We have seen a couple, and heard or read about others.  While not an everyday occurrence, when it does happen the results are devastation with broken rods and/or crankshafts and split cylinders.  Not pretty.