986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Catch Can instead of the AOS...anyone tried it yet?!

Jake Raby · 08-11-2009, 06:55 AM

I had one track car with an AOS failure twice in the same day.. The second failure was a brand new AOS.

I have zero tolerance for something that fails and can dump oil on the track, or worse yet cause a fireball behind me like what I experienced last week on a test drive when the AOS went and the engine back fired and lit up all the oil vapors.

I'd only recommend AOS omission on track cars, it would not be legal in most areas for street cars due to emissions requirements, anyway...

A part failing once is OK, twice is not acceptable and anything more than that and its pure insanity as you are expecting a different outcome from doing the same thing over and over...

I have also experienced failed AOS units that caused low oil pressure as they allowed the intake charge to pull too much vacuum on the crankcase, thus pulling oil from the pick up tube and even getting so bad that main bearings squealed! When this happened there was ZERO smoke out the back of the car and the vacuum was so great that it sucked the front and rear seals further into the case and totally collapsed the oil filler tube.

It took us a day to figure out it was an AOS failure, so there are two different modes of failure of the AOS and this more rare, second type of failure can easily cause an engine failure due to oil starvation.. I am now exploring the possibilities of some oil starvation engine failures we have seen have actually been directly related to AOS failure and nothing else.

At leat with the AOS bypassed the chances of this occuring are zero as the function of the two systems are totally separated.

08-11-2009, 06:55 AM	#8
Jake Raby Engine Surgeon Join Date: Aug 2008 Location: Cleveland GA USA Posts: 2,425	I had one track car with an AOS failure twice in the same day.. The second failure was a brand new AOS. I have zero tolerance for something that fails and can dump oil on the track, or worse yet cause a fireball behind me like what I experienced last week on a test drive when the AOS went and the engine back fired and lit up all the oil vapors. I'd only recommend AOS omission on track cars, it would not be legal in most areas for street cars due to emissions requirements, anyway... A part failing once is OK, twice is not acceptable and anything more than that and its pure insanity as you are expecting a different outcome from doing the same thing over and over... I have also experienced failed AOS units that caused low oil pressure as they allowed the intake charge to pull too much vacuum on the crankcase, thus pulling oil from the pick up tube and even getting so bad that main bearings squealed! When this happened there was ZERO smoke out the back of the car and the vacuum was so great that it sucked the front and rear seals further into the case and totally collapsed the oil filler tube. It took us a day to figure out it was an AOS failure, so there are two different modes of failure of the AOS and this more rare, second type of failure can easily cause an engine failure due to oil starvation.. I am now exploring the possibilities of some oil starvation engine failures we have seen have actually been directly related to AOS failure and nothing else. At leat with the AOS bypassed the chances of this occuring are zero as the function of the two systems are totally separated. Last edited by Jake Raby; 08-11-2009 at 07:01 AM.