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I too suspect crankcase pressure is the culprit


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A friend who is not active on the web has a frustrating problem with his 1997 Boxster. The car has about 60,000 miles, Tiptronic, but with an aftermarket supercharger. Car has run beautifully for several years. About 2 years ago the AOS failed and was replaced with a Porsche part along with all AOS hoses. At the time the hoses seeped a little oil, but nothing significant. Now, with less than 1,500 miles added, the AOS has failed once more. His mechanic replaced it once again with a Porsche part, and the oil seepage has continued to occur. The mechanic, who is knowledgeable, is baffled and the owner is frustrated. We have speculated that the supercharger may be creating excessive crankcase pressure, and we might expect this on a 100k + engine. Can anyone shed light on possibilities.
Grasping at straws, if the pressure will continue to cause AOS failures, is there a potential solution in installing a traditional PCV valve and a catch can?
These engines really were not meant to be supercharged or turbo charged.
The OEM compression ratio is 11.5:1 which is too high to charge.
Many have installed catch cans and valves but I haven't heard of one that was satisfied with their solution.
Happy Boxstering,
Pedro

Pedro Bonilla 1998 Boxster 986 - 287,000+ miles: http://www.PedrosGarage.com
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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Pedro (Weston, FL)
These engines really were not meant to be supercharged or turbo charged.
The OEM compression ratio is 11.5:1 which is too high to charge.
Many have installed catch cans and valves but I haven't heard of one that was satisfied with their solution.
Happy Boxstering,
Pedro

Thank you. This was my concern, but I'm not a mechanic, and far from knowledgeable. My friends who are currently waterlogged at the BRBS have sung your praises often.
I have a similar chronic oil problem on my track car. It existed with the old (very worn) motor, and continues with the newly rebuilt one. runs great, but uses a constant stream of oil - 1 qt/1k on the road and 3/8 qt/track day (2+ hours, WOT) on the track.

I cant prove much, but i suspect the AOS is overwhelmed.

The question on your friend's car is "what changed?". Either a) it just got old and has more blow-by or b) something else changed.

I do have a question. The supercharger pressurizes the intake. The intake generally has the vacuum to vent the crankcase through he AOS. Now that you have pressure, not vacuum, how does that work?

Grant

Grant gee-lenahan-at-vee-eff-email-dot-net
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RWP
A friend who is not active on the web has a frustrating problem with his 1997 Boxster. The car has about 60,000 miles, Tiptronic, but with an aftermarket supercharger. Car has run beautifully for several years. About 2 years ago the AOS failed and was replaced with a Porsche part along with all AOS hoses. At the time the hoses seeped a little oil, but nothing significant. Now, with less than 1,500 miles added, the AOS has failed once more. His mechanic replaced it once again with a Porsche part, and the oil seepage has continued to occur. The mechanic, who is knowledgeable, is baffled and the owner is frustrated. We have speculated that the supercharger may be creating excessive crankcase pressure, and we might expect this on a 100k + engine. Can anyone shed light on possibilities.
Grasping at straws, if the pressure will continue to cause AOS failures, is there a potential solution in installing a traditional PCV valve and a catch can?

It is possible the supercharger pressure control system is over pressurizing the engine but I think the engine would blow before the AOS.

More than likely the PCV is stuck and unable to close -- via a spring -- to prevent the crankcase from being over pressurized from high intake manifold pressures that are of course the result of supercharging. (In a N/A engine the PCV is there to also prevent over pressurization in the event of a back fire into the intake manifold.)

My 2nd hand in is getting to and replacing the PCV is about as hard as it is to replace the AOS.

A Porsche tech might actually remove the intake manifold as this makes access to the PCV easier. There are a lot of easy to damage aged/fragile hoses/connectors that one might break while fighting with the PCV.

If you elect to replace the PCV you probably will want to replace the AOS as it has probably been sent well on its way to a premature failure.
You may also want to contact the folks at TPC. They are the ones providing the supercharges for the Boxster engines. They may have some ideas.
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