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Vacuum leak coming from dipstick - normal AOS integrity?

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Old 03-20-2014, 06:48 PM
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odonnell
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Default Vacuum leak coming from dipstick - normal AOS integrity?

I rigged up a PVC fitting to pressurize my intake system from the AFM up, and found a leak from the top of the dipstick - it's loud enough to hear from the cabin. When I push down hard on it, it stops temporarily. When I pull the dipstick out slightly, air whooshes out.

Obviously this needs attention, but does my AOS also need to be addressed? I'm not sure if this is normal or not. I have no oil or milkshake in my J-boot or throttle body, so I've always assumed the two seals were good.

Thanks for all pointers/clarification!

(oh, and if anyone has a known-good dipstick they wouldn't mind selling, PM me)
Old 03-20-2014, 06:56 PM
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william_b_noble
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the o-ring on the dipstick and on the bottom of the tube are supposed to be common failure points.
Old 03-20-2014, 07:26 PM
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odonnell
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I intend to re-seal the AOS when I'm doing intake manifold gaskets and TB reseal (this weekend) plus a million other WYIT things.

On my car, the only rubber seal for the dipstick that I can see is the one right under the gripping ring:

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...which looks like it is a little worn down.
Old 03-20-2014, 08:42 PM
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John_AZ
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On my '87 924s there is an O-ring at the bottom of the dipstick tube to oil pan.
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Old 03-20-2014, 11:55 PM
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konakat
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There are no seals on the early cars' dipstick tubes. I don't know if that means that it is okay if they leak, but I went ahead and bought a replacement for $20 on ebay. As far as I can tell they are all compatible at least up through '87. I bought one from a turbo myself, then ordered the o-ring for it. Went on with no trouble. You basically need the top two hits from this search http://www.autoatlanta.com/Porsche-9...Tube-srch.html

As you can see in the picture, the dipstick tube has a lip an inch or two from the bottom that the o-ring can sit against. Our cars just have a smooth tube so an o-ring won't stay in place.
Old 03-21-2014, 01:17 AM
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odonnell
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Thanks! I'd love to skip the $50 price tag though

Also, I have an update which may or may not matter. I ran the engine and pulled the dipstick, and the idle changed very slightly - almost imperceivable. When I revved the engine (which usually creates a leaky whine) it still made the noise, despite the dipstick being out

Starting to wonder what the problem really is. I have lackluster acceleration, and a known leak at the dipstick, that somehow isn't really affected if the dipstick is even in or not.
Old 03-21-2014, 10:07 AM
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konakat
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I only spent $20 for mine on ebay. You could try gooping some ATV at the bottom of the dipstick tube just to see if that makes a difference. It doesn't surprise me that pulling the dipstick out didn't matter, you already have a big leak, you just made it bigger.
Old 03-21-2014, 10:52 AM
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John_AZ
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Originally Posted by sausagehacker
I rigged up a PVC fitting to pressurize my intake system from the AFM up, and found a leak from the top of the dipstick - it's loud enough to hear from the cabin. When I push down hard on it, it stops temporarily. When I pull the dipstick out slightly, air whooshes out.
Since you are searching for common leaks, you should rebuild your TB throttle body. The throttle body shaft seals that pivot the butterfly are usually dried out.

http://www.arnnworx.com/catalog/inde...949680607ce769

J_AZ
Old 03-21-2014, 10:55 AM
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odonnell
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Already got it, it's happening later today!

I'm gonna get a rubber stopper to plug the dipstick hole and see what happens.



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