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New AOS failed out of the box. Possible?


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I've recently replaced my AOS as one of the preventive maintenance items. My old one was fine and created ~5" water vacuum measued by a digital manometer at the oil filler cap (I made an adaptor out of an old cap). I just did the same measurement after the new AOS and to my surprise, it read ~9" water vacuum! All measured at idle after engine is fully warmed up. My understanding is the AOS has a spring loaded diaphragm inside that regulates the vacuum (sourced from the throttle body) to maintain ~5" water vacuum in the crankcase.

So the only explanation of this high vacuum reading is the new AOS somehow has a weaker spring or a leak that allows more vacuum to "go through". Has anyone experienced this?

So much for PM :(

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Loren, John, and others, any experience with this type of "failure" or at least out of norm operating point?

 

BTW, I verified my manometer against a home-made manometer (some tubing + water) and confirmed the manometer is extremely accurate. I should also mention that I've also replaced the following:

 

- dipstick tube o-ring and the oil filler tube o-ring. They seem to be leaking a bit (oil stain/dirt around the areas)

- the 3 o-rings on the two AOS vent tubes. The 4th one is under the bank 2 intake manifold so I didn't replace it

- the vacuum reservoir, which had a small leak at the bottom of it but I don't think that will increase the crankcase vacuum at all.

 

So overall the crankcase and AOS are sealing better, not sure if that contributes to higher crankcase vacuum though. Thoughts?

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Loren, John, and others, any experience with this type of "failure" or at least out of norm operating point?

 

BTW, I verified my manometer against a home-made manometer (some tubing + water) and confirmed the manometer is extremely accurate. I should also mention that I've also replaced the following:

 

- dipstick tube o-ring and the oil filler tube o-ring. They seem to be leaking a bit (oil stain/dirt around the areas)

- the 3 o-rings on the two AOS vent tubes. The 4th one is under the bank 2 intake manifold so I didn't replace it

- the vacuum reservoir, which had a small leak at the bottom of it but I don't think that will increase the crankcase vacuum at all.

 

So overall the crankcase and AOS are sealing better, not sure if that contributes to higher crankcase vacuum though. Thoughts?

 

I'm not sure what you are seeing, unless the new unit has a problem.  Normally, we see around 5 inches of water on a good AOS.  And while I have never seen a new one that was off right out of the box, that does not mean it cannot happen.

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  • 3 weeks later...

It's the stock standard version AOS from Sunset Porsche. The old one was also stock.

 

1. Can you confirm the part number used is a 996.107.023.55?

2. Copied from the Pelican AOS Tech Article: "When the air-oil separator fails, the intake manifold vacuum will draw into the crankcase and the levels will reach 9-12 inches or more."

3. I would replace it with another new one since it is not worth saving the $150 for the problems it will create. At a minimum, I would take the new one out it out to test the non-coolant ports with a mityvac.

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1. No, mine is 99610702651, which is the correct one for MkII (my car is a '03 C2) AFAIK

2. Yeah, I was aware of that article but still puzzled why a brand new AOS will fail

3. Actually I had tested it like you suggested before I installed it. I got the same ~10" H2O reading but thought maybe that's not the proper way to test it because the final crankcase pressure (regulated by the AOS) also depends on the air flow from crankcase to the AOS and the natural crankcase pressure without the AOS. I have no ways to simulate those. Is my thinking correct?

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  • 1 month later...

Update: after ~1,000 miles, the crankcase vacuum went up to 24" H2O so I decided to swap a new one it. Took only 4hrs this time including a 15min break. Also took the opportunity to replace some spring type hose clamps on the AOS with OE spring clamps. Crankcase vacuum is a very nice 4~5" H2O now and I'm happy.

Still not sure why the previous new one was bad out of the box. May do a post mortem later when I have time.

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  • 5 months later...

Ahsai,,

I also have a 2003 C2 (a Cabriolet). I am experiencing a challenging removal of the final bolt of the upper air intake.  It seems that the round face of the AOS sits directly above the bolt head.  Can you please share how you removed that bolt?

 

And to clarify, my AOS is the newer part that does not have a bellows.  I see too that the older AOS that has the bellows has two bolts that are horizontal into the block; the newer AOS has two mounting bolts that are positioned vertically into the block.  

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