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Discussion Starter #1
In the never ending quest to figure out my oil consumption issue I recalled someone saying that if your oil cap is hard to get off because there is vacuum to it that your AOS/VOS diaphram is likely bad, that there should be little to no vacuum in the crankcase.

So here's what I did tonight, please repeat this test and report your results.

Begin with car cold

Step 1: Open Hatch
Step 2: Open oil door flap (but leave cap on tight)
Step 3: Start engine
Step 4: Immediately get out of car and go around and remove the oil cap.
Step 5: Report results here!


In my case I was able to take the cap off, but it WAS under quite a bit of vacuum. Once I took it off the car ran like ****, it sputtered, the rpm's dropped and I believe would have died had I not put the cap back on so the RPM's would come back and engine smooth out. I took the cap off again, car ran like ****, put the cap on, car ran great.

Does this happen to everyone else, or does your car run fine with the cap off? I don't want to report this as a problem to the dealer until I've had a chance to check what happens with other Cayman owners.

Thanks in advance for your reports on this subject!
:thanks:
 

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I am headed out to the garage anyway, so I will play along. When you say "start with the car cold", it is about 30 degrees in my garage and about 20 degrees outside right now. So to do your test the car will be idling at the higher rpm.

That ok?
 

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Discussion Starter #3
I am headed out to the garage anyway, so I will play along. When you say "start with the car cold", it is about 30 degrees in my garage and about 20 degrees outside right now. So to do your test the car will be idling at the higher rpm.

That ok?
Yes that's fine, it was about 40 in my garage, so yes the car shold be idling faster than normal because it is in the warm-up cycle. Even with the car idling fast when I removed the cap it about killed the car.
 

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Ok... my less than scientific results:

started, as discussed it was idling higher because of the warm up.

I removed the oil fill cap, and did not feel any vacuum. The cars idle got rough, but was not anywhere near cutting off. I replaced the cap after about 15 seconds. I let it sit for 25 seconds and removed the cap again. Still no vacuum and same result with the idle. I let it sit until the idle dropped to its normal idle speed and removed the cap again. Still no vacuum, and this time the idle got a little rougher, but not as bad as the first two attempts.

Seems like there must be a small vacuum, how else can removing the oil fill cap effect the idle? Perhaps mine has a much lower vacuum level?

Hope that helps!
 

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Completely cold, I ran the test and could feel a slight vacuum. Car idled a bit rough but was not dying at all. I took video. The first time I could not get the cap off. I used some channel lock pliers to loosen the cap. Hilarious. Youtube is in "read only mode" so it may take a while to publish.
 

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K-man,

I just performed the steps and the results are the same as dave and ghoster. Idle was a little rougher but no where near cutting out. Definitely felt the vacuum. As info I live in south florida so quite a but warmer. Not sure if temp skews the test but I wouldn't think so. j.r.
 

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Does this happen to everyone else, or does your car run fine with the cap off? I don't want to report this as a problem to the dealer until I've had a chance to check what happens with other Cayman owners.
!
:thanks:
I think it is normal for the car to idle rough with the oil cap open. I did not do this on my Cayman, but I tried this with my other cars in the past. hope this helps.
 

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On a carborated car, there is supposed to be a slight vacuum to route crank-case gases back into the combustion chambers, for emissions. Isn't that what the PCV value controls. I suspect injected engines do the same thing.
Removing the oil cap is effectively creating a vacuum leak, thus the rough idle.

I only have a rudamentary understanding of the process, but I think that's what is going on.
 

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I think it is normal for the car to idle rough with the oil cap open. I did not do this on my Cayman, but I tried this with my other cars in the past. hope this helps.
I think so too... My 911 (CIS injection) does that too.. it drops a few hundred rpms with the cap off, that's why it sounds rough... Will try the CS tonight.
 

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Just did it, the car was in the garage, it's about 38F outside, started from cold.
With the oil cap off, there was vacuum pressure against the cap, BUT, unlike others, my RPM actually rose with the cap off.
Not sure why it would do that, when others have seen a rough running engine. I expected a "loping" RPM register.
 

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Discussion Starter #14
sounds like faulty PCV ken, happens on 2.0t engines all the time... Is the car running in closed loop? How is your idle?

Casey
How do I tell if it is running in closed loop? The idle normally isn't bad, the issues I've been having are 2 different issues, one long standing, the other recent.

The long standing issue is the oil consumption since the engine rebuild and installation of the motorsport VOS. Apparently from recent investigation by my Porsche tech it is getting sucked into the throttle body coming from the VOS and burned through the engine.

The more recent issue is the random dying when coming to a stop at a stoplight, stop sign, etc.

I'm trying to solve issue #1 first, but it might be that issue #2 is related. Issue #2 never happened before until I got my car back from TPC. TPC didn't do anything unusual though other than a leak down test and changing out spark plugs.
 

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I agree with the others who state that it's normal for engines to run poorly with the oil cap off. It even happens with my Toyota. There is vacuum in the crankcase so that the oil and blowby vapors get sucked back into the engine and get burned off, rather than venting to the atmosphere. This means that when you have the oil cap off you have a big vacuum leak, and we all know how poorly cars run with vacuum leaks.

The point of the VOS is to separate liquid oil from oil vapors. The liquid oil is returned to the pan and the vapors are burned off. My understanding is that when the VOS fails, liquid oil no longer gets returned to the pan, but instead follows the path of the vapors and gets burned off.
 

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Discussion Starter #16
I agree that I would expect the engine to not run right with the oil cap off, but man it was really bad. I'm wondering if my Motorsport VOS was bad from the beginning? I never had any clouds of smoke on the track from ingestion, but its been constantly sucking oil along with vapors into the motor to the tune of using a quart every 4-500 miles.

I guess the only way to see if that's really the problem is to take it out and replace it with either my original one (if I can find it) or another one, I would lean towards another one since my original one allowed me to get oil ingestion at the track.
 

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I can tell you that if you start a GenII car with the oil cap off it will run poorly just as you describe, and trigger a CEL.
 

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I just did the test, my result is the same as Ken's. Scary... What can be happened though?
 

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No experience with this on the Porsche but on my last car (BMW 740iL), heavy suction/vacuum at the oil dipstick is the symptom of a bad oil separator valve.
Is there a similar device on the flat 6?
 

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In the never ending quest to figure out my oil consumption issue I recalled someone saying that if your oil cap is hard to get off because there is vacuum to it that your AOS/VOS diaphram is likely bad, that there should be little to no vacuum in the crankcase.

So here's what I did tonight, please repeat this test and report your results.

Begin with car cold

Step 1: Open Hatch
Step 2: Open oil door flap (but leave cap on tight)
Step 3: Start engine
Step 4: Immediately get out of car and go around and remove the oil cap.
Step 5: Report results here!


In my case I was able to take the cap off, but it WAS under quite a bit of vacuum. Once I took it off the car ran like ****, it sputtered, the rpm's dropped and I believe would have died had I not put the cap back on so the RPM's would come back and engine smooth out. I took the cap off again, car ran like ****, put the cap on, car ran great.

Does this happen to everyone else, or does your car run fine with the cap off? I don't want to report this as a problem to the dealer until I've had a chance to check what happens with other Cayman owners.

Thanks in advance for your reports on this subject!
:thanks:
OK Ken here are some -

DIFFERENT RESULTS

As you know I have the same year as you, but no real changes to the basic intake system or exhaust. Was d-snorked and that's about it. Have had zero problems with the engine. Engine NEVER needs oil added - oil was changed about a month ago.

27 degrees this morning.

Started easily, no excessive smoke. Running great.

Got out - removed oil cap, engine actually increased speed - did NOT seem to be running worse though - maybe better, but at least higher rpm's - did notice a slight vacuum as I removed cap.

Put cap back on and - WOW - The car spat out that huge plume of white smoke that everyone talks about. Covered at least half my yard. It continued to put out excessive smoke for at least 30 seconds or so.

Got in the car and drove - by the time I got past my neighbors house the exhaust seemed mostly normal - maybe still a little smoky. By the first stoplight it was invisible from the front of the car. Fine after that.

So, guess I have now seen that white smoke you all talk about. My senses (smell, etc.) and other experience make me think it was a water vapor based plume this morning.

But you folks that are more expert on the Prosche 3.4 engine than I - please tell me what you think...
 
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