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Join Date: Apr 2011
Posts: 1
Question PCV System Replacement

Dear Pelican BBS Boxster enthusiasts - I have a 2000 Boxster S with ~70K miles. I drive it about 7.5K miles each year for commuting to work. Recently, the car developed a ringing noise in the engine compartment upon cold start (like a fly wheel contacting another piece of metal at high speed) and emitting huge plumes of white smoke. I took it to a local shop I have used for several years and they informed me that the PCV system seals had failed. They said pressure developed in the engine forcing oil through and out the exhaust. The technician said that the smoke was white because the oil was condensed with water vapor in the engine. The PCV system needs to be replaced and the cost estimate was $1500, primarily due to 10 hrs. of labor. The shop also said that the mass O2 sensors may have been damaged by the oil and that a new catalytic convertor might also be needed. The ringing noise went unexplained. I should note that all this occurred after the same shop did a replacement of the motor and tranny mounts for me at a cost of ~$700. I am posting this message to see if any one else has experienced a similar problem with PCV seal failure and oil pressure issues. I am also interested to know if the time estimate for the system replacement is reasonable. The shop informed me that the car would need to go through several drive cycles after the PCV repair in order to determine if the mass O2 sensors were throwing readings. Thanks to all for any input./Dave Kaber
Old 04-09-2011, 10:01 AM
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Author of "101 Projects"
Wayne 962's Avatar
Hi Dave. Welcome to the forums! Two minutes after you post your question, I am here to assist!

What you might have here is an air-oil separator problem. This device sucks air out of the crankcase and then funnels it back into the engine intake so that fumes from inside the engine can be burned again, instead of being released to the atmosphere. It's an emissions device.

I have a complete article on replacing it right here: Pelican Technical Article: Boxster Air / Oil Separator Replacement - 986 / 987 Take a look at the article, and it should give you an idea of what is involved.

As for the replacement costs, 10 hours is completely ridiculous in my opinion. I'm thinking that your shop has never done this before, and is probably quoting you high to cover their butt. As for the 02 sensors, it's not so much that the O2 sensors get messed up, but the catalytic converters might too. What you need to do is to replace the air-oil separator unit and then run the car for several hundred miles to burn all of the crap out that may have entered the exhaust. Then you check to make sure that everything is working properly.

As for the loud "ringing noise", I have never heard this noise myself, but I am told that it's caused by air getting sucked into the engine through some of the seals. When the air-oil separator fails, it takes the intake manifold vacuum (which is quite powerful - it is used to power the power brakes for example), and starts sucking on the internals of the engine. This causes air to want to seep into the engine through various seals (which may be old and may have some areas where air can leak by). This intake vacuum on the engine case can cause this high pitched "whistle", as I have heard it most commonly described.

Let me know if you have any more questions!

Wayne R. Dempsey, Founder, Pelican Parts Inc., and Author of:
101 Projects for Your BMW 3-Series 101 Projects for Your Porsche 911 How to Rebuild & Modify Porsche 911 Engines 101 Projects for Your Porsche Boxster & Cayman 101 Projects for Your Porsche 996 / 997
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SPEED READ: Porsche 911 (October 2018)
Old 04-09-2011, 10:09 AM
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Join Date: Nov 2008
Location: Sanford NC
Posts: 1,245
AOS and tube replace. (This is the equivalent of the PCV system) Instructions available online. (I just got a quote for $695 parts and labor)

Throttle body clean. Get oil out of intake so you start getting clean exhaust to burn off the sensors and cats. Instructions available online.

Clear any codes

Run for a while...several heat and cool cycles and say 100 miles or so.

If you do need new O2 sensors, buy Bosch part(s) just like Porsche does (saves $, same part) and do it yourself or have a muffler shop do it for you ($50 labor for one)...but only do it if codes tell you you need to. (parts list available online)

Cats...probably not.
Old 04-09-2011, 03:47 PM
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Join Date: Mar 2011
Location: SF-BayArea CA
Posts: 63
When I open the oil filler cap on my 986 there seems to be a little bit of pressure that's built up.
Would that be a failing AOS?
Old 04-12-2011, 09:56 AM
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Author of "101 Projects"
Wayne 962's Avatar
Nope. A little bit of vacuum is okay. Typically when the air oil separator fails, it produces vacuum that is so high that you often cannot even summon enough force to remove the oil cap.

Old 04-12-2011, 03:08 PM
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