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Sweating oil on intake resonance tube


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Hello everyone, the other day I was trying to swap voltage regulator on the back of alternator and noticed that wires coming from the alternator were covered in oil.

It seems to come from resonance tube or whatever the big rubber connector to intake distirbutor is called (between intake and throttle). Hose clamps were positioned so that their bolts were on the bottom so oil sweats and drops from there. Not much (certainly not leaking) but wanted to check if it could be a sign of oncoming problem.

thanks in advance

2003 996 c4s

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Hello everyone, the other day I was trying to swap voltage regulator on the back of alternator and noticed that wires coming from the alternator were covered in oil.

It seems to come from resonance tube or whatever the big rubber connector to intake distirbutor is called (between intake and throttle). Hose clamps were positioned so that their bolts were on the bottom so oil sweats and drops from there. Not much (certainly not leaking) but wanted to check if it could be a sign of oncoming problem.

thanks in advance

2003 996 c4s

Mine is similar. Oil sweats but no drops. My AOS was replaced by dealer a few yrs ago when my car ('03) was still under factory warranty because I complained about high oil consumption (1 quart per 1400 miles) and I didn't know it was not uncommon for these engines to consume that much at the time.

However, the oil sweat returned not long after AOS replacement and my car is still consuming oil at the same rate. How much oil does your engine consume? I'm speculating that my oil consumption is because of oily air from the AOS get sucked into the throttle body and the new AOS unit the dealer put in was also defective.

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Hello everyone, the other day I was trying to swap voltage regulator on the back of alternator and noticed that wires coming from the alternator were covered in oil.

It seems to come from resonance tube or whatever the big rubber connector to intake distirbutor is called (between intake and throttle). Hose clamps were positioned so that their bolts were on the bottom so oil sweats and drops from there. Not much (certainly not leaking) but wanted to check if it could be a sign of oncoming problem.

thanks in advance

2003 996 c4s

Mine is similar. Oil sweats but no drops. My AOS was replaced by dealer a few yrs ago when my car ('03) was still under factory warranty because I complained about high oil consumption (1 quart per 1400 miles) and I didn't know it was not uncommon for these engines to consume that much at the time.

However, the oil sweat returned not long after AOS replacement and my car is still consuming oil at the same rate. How much oil does your engine consume? I'm speculating that my oil consumption is because of oily air from the AOS get sucked into the throttle body and the new AOS unit the dealer put in was also defective.

My 2003 uses a quart every 5000 miles.

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Hello everyone, the other day I was trying to swap voltage regulator on the back of alternator and noticed that wires coming from the alternator were covered in oil.

It seems to come from resonance tube or whatever the big rubber connector to intake distirbutor is called (between intake and throttle). Hose clamps were positioned so that their bolts were on the bottom so oil sweats and drops from there. Not much (certainly not leaking) but wanted to check if it could be a sign of oncoming problem.

thanks in advance

2003 996 c4s

Mine is similar. Oil sweats but no drops. My AOS was replaced by dealer a few yrs ago when my car ('03) was still under factory warranty because I complained about high oil consumption (1 quart per 1400 miles) and I didn't know it was not uncommon for these engines to consume that much at the time.

However, the oil sweat returned not long after AOS replacement and my car is still consuming oil at the same rate. How much oil does your engine consume? I'm speculating that my oil consumption is because of oily air from the AOS get sucked into the throttle body and the new AOS unit the dealer put in was also defective.

My 2003 uses a quart every 5000 miles.

That's pretty good. Thanks for the info.

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  • 1 year later...

I've attached a picture of my 02-996-Cabby resonance intake tube "weeping" @ 64K miles. I have no fault code on my durametric reader and no smoke. I do consume a very minimal amount of oil, but I haven't yet kept track of the actual amount. Like others, I am suspecting the AOS is beginning to fail, and I am wondering if anyone knows an "actual value" on the durametric tool that might assist in this diagnosis, (perhaps something to do with airflow values?) I do understand the integrity tests for the AOS that have been posted herein, but in the absence of other symptoms, I'm not likely to do all that quite yet.

post-85898-0-69795000-1367260531_thumb.j

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The Durametric is not going to provide definitive data indicating that the AOS is on the way out; you best bet is to try and remove the oil filler cap while idling. If the cap comes off with little effort, the AOS is fine; but if it takes a lot of force to remove it due to high case vacuum, the AOS is toast.

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I checked the oil cap after a 1/2 hour drive this morning. It came off quite easily (as normal) but I felt a "very slight" suction, and I noticed a slight increase in engine idle RPM, but still very smooth idle. Does that tell me anything about the AOS?

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Crankcase vacuum is normally far less than intake vacuum.

I suppose perhaps in the case of a gross intake leak, where vacuum is greatly reduced perhaps the AOS cant do it's job as well???

But then you would notice the engine running really very poorly.

In any case, there is a very definitive test for the AOS... (or at least crankcase vacuum) and here it is:

http://www.renntech.org/forums/tutorials/article/255-an-inexpensive-way-to-test-for-a-bad-aos/

Edited by logray
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I checked the oil cap after a 1/2 hour drive this morning. It came off quite easily (as normal) but I felt a "very slight" suction, and I noticed a slight increase in engine idle RPM, but still very smooth idle. Does that tell me anything about the AOS?

Sounds like you are fine. A normal AOS gives you a vacuum level of about 5 inches of water, basically the slight suction you felt. When they fail, the vacuum level jumps to several times that level, making the cap nearly impossible to get off.

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Crankcase vacuum is normally far less than intake vacuum.

I suppose perhaps in the case of a gross intake leak, where vacuum is greatly reduced perhaps the AOS cant do it's job as well???

But then you would notice the engine running really very poorly.

In any case, there is a very definitive test for the AOS... (or at least crankcase vacuum) and here it is:

http://www.renntech.org/forums/tutorials/article/255-an-inexpensive-way-to-test-for-a-bad-aos/

Thanks, Logray. Yes, I've done what you did but less elegantly as your setup :) Mine is about 6in H2O so it's normal. My car always burns 1 quart / 1400 miles, even when new. Now it has about 54k miles. I just think that oil gets sucked into the intake from AOS, as opposed to seeping through the oil rings....just a theory.

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Both happen actually... 1 qt / 1400 is not abnormal.

I'm at 1qt per 2000 miles with new rings, and I probably could have done better with the breakin. I might redo the rings at some point.

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