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Squealing from engine- AOS or bearing?


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2004 Boxster S. My engine started squealing on the way into work this morning- a horrible squeal that sounded like the serpentine belt slipping; stopped and started for a bit; generally went away when I revved the engine. It *sounded* like the sound was coming from the mid/lower right side of the engine- power steering pump? The belt isn't slipping and none of the pulleys appear siezed. However, I don't have a 24mm socket here and am unable to loosen the serpentine belt to verify all the pumps and pulleys are spinning freely. There is no white smoke, and no CEL, though I did see one tiny puff of white smoke a few weeks ago on startup (I know it's normal and thought nothing of it) and one CEL a month or so ago that came on and went away and never came back.

Troubleshooting seems consistant with AOS- I couldn't remove the oil cap while the engine was running, and struggled to get it off 10 minutes later. I did not hear the sound while the cap was removed, but heard a LOT of air whooshing through it. After about two minutes, got billowing clouds of white smoke. Wasn't sure if that was normal to see with the oil cap removed, or if it's "a sign".

Q: Does this sounds like DEFINITELY AOS?

Q: Can I safely drive home on it? 20 miles, maybe 45 minutes in rush hour traffic, though I may cut off a little early today to lessen my time in traffic.

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For me, it did gave sign but I ignored it thinking the mild smoke was seepage through the cylinders. On that same day, made several stop and go, massive plume of white smoke on freeway and had to pull over and gotten it towed home.

I would check the tube that goes to the intake to see if there are significant amt of oil. I believe, generally, it should be dry w/ minimal-to-none of oil residue but don't quote me on it.

01 based model w/ ~41K miles.

Edited by Trey T
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2004 Boxster S. My engine started squealing on the way into work this morning- a horrible squeal that sounded like the serpentine belt slipping; stopped and started for a bit; generally went away when I revved the engine. It *sounded* like the sound was coming from the mid/lower right side of the engine- power steering pump? The belt isn't slipping and none of the pulleys appear siezed. However, I don't have a 24mm socket here and am unable to loosen the serpentine belt to verify all the pumps and pulleys are spinning freely. There is no white smoke, and no CEL, though I did see one tiny puff of white smoke a few weeks ago on startup (I know it's normal and thought nothing of it) and one CEL a month or so ago that came on and went away and never came back.

Troubleshooting seems consistant with AOS- I couldn't remove the oil cap while the engine was running, and struggled to get it off 10 minutes later. I did not hear the sound while the cap was removed, but heard a LOT of air whooshing through it. After about two minutes, got billowing clouds of white smoke. Wasn't sure if that was normal to see with the oil cap removed, or if it's "a sign".

Q: Does this sounds like DEFINITELY AOS?

Q: Can I safely drive home on it? 20 miles, maybe 45 minutes in rush hour traffic, though I may cut off a little early today to lessen my time in traffic.

Difficulty in removing the oil cap with the engine running is a classic sign of AOS failure.

As suggested by Trey, inspect for oil in the "J-tube" and in the throttle body. If you find a more than very minimal amount of oil in those, you should be leery of driving it at all, unless you are not risk averse. There is the possibility of Hydrolock with a "broken" AOS and that will make your engine toast in very short order, so be careful.

Regards, Maurice.

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Risk averse? Bah, I drove my old camaro with a bad head gasket until it hydrolocked... 4 years and a lot of coolant later! No additional damage from the hydrolock, fortunately. As luck would have it, I finally finished replacing the headgasket (and then tearing it back down to readjust the valves I'd overtightened, ugh) two weeks ago- I can drive it to work tomorrow & pick up the new AOS instead of having to steal my wife's car for the day.

I made it home safely, by the way. It smoked like mad, but I think it was only oil that got sucked in when I pulled the oil cap to test it this morning, but MAN what a smokescreen! Cleared up after about 5 miles at which point it started squealing. I'm pretty confident it's the AOS, now. Gonna go ahead and pull the old one tonight, I think. I don't have to drain the oil or anything for this, do I? The only oil to clean up is what's coating the inside of the AOS?

Edited by grover
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you do not need to drain oil. you can take off your manifold, runners, and throttle body to clean if you want but I didn't have the patience and time. I just let it idle for ~30min and rove around a bit b4 I put it back on the road.

get a generic hose clamp to attach the tube to the engine-side when you replace your AOS. i'm 5'11" and I got scraped and bruise trying to use OEM clamp and was unsuccessful.

Edited by Trey T
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you do not need to drain oil. you can take off your manifold, runners, and throttle body to clean if you want but I didn't have the patience and time. I just let it idle for ~30min and rove around a bit b4 I put it back on the road.

get a generic hose clamp to attach the tube to the engine-side when you replace your AOS. i'm 5'11" and I got scraped and bruise trying to use OEM clamp and was unsuccessful.

Thanks. There wasn't any smoke the last 20 minutes or so of my ride, just squealing, so I should be good with that respect. I'm buying a new boot and will just cut the old one in half if I need to :) I'll have to see if I have any pipe clamps; I'm pretty sure I've got some laying around, but have to figure out where I put them!
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Risk averse? Bah, I drove my old camaro with a bad head gasket until it hydrolocked... 4 years and a lot of coolant later! No additional damage from the hydrolock, fortunately. As luck would have it, I finally finished replacing the headgasket (and then tearing it back down to readjust the valves I'd overtightened, ugh) two weeks ago- I can drive it to work tomorrow & pick up the new AOS instead of having to steal my wife's car for the day.

I made it home safely, by the way. It smoked like mad, but I think it was only oil that got sucked in when I pulled the oil cap to test it this morning, but MAN what a smokescreen! Cleared up after about 5 miles at which point it started squealing. I'm pretty confident it's the AOS, now. Gonna go ahead and pull the old one tonight, I think. I don't have to drain the oil or anything for this, do I? The only oil to clean up is what's coating the inside of the AOS?

Full steam ahead, then...

Since "it smoked like mad", you have now added to the to probability that your diagnosis is correct! clapping.gif

Here is a great DIY for cleaning the throttle body from Pedro's Garage: http://pedrosgarage....ottle_Body.html

Reinstalling the factory-style clamp on the bottom of the bellows tube is just a matter of getting just the right angle of attack from underneath the right rear rotor (with the rim removed) with the car jacked up at just the right height. Here's a photo of the view that that angle will provide with the red arrows showing the two 10mm bolts and the yellow arrow pointing to the bellows:

post-6627-091403100 1279656396_thumb.jpg

(Note that in this photo, the bottom OEM clamp has been squeezed and tied up with strong zip ties to hold it open for installation)

Here it is installed:

post-6627-051096700 1279656986_thumb.jpg

Here is a tool I learned about here on RennTech (from Tool Pants) that made the next job much easier.

post-6627-060417600 1279658263_thumb.jpg

(Available from Porsche.)

Good luck!

Regards, Maurice.

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Here you go, full docs on the air-oil separator replacement: http://www.pelicanpa...l_Separator.htm

If you remove the oil cap while the car is running and the noise goes away, then it's most likely the air-oil separator.

-Wayne

Well, joy. My AOS is not the model shown on the pelican parts page, or Mike Focke's, though it does look just like the photo Mike posts where he says 03/04 are different. On mine, the bolts are accessed from the top, and the bottom half looks significantly different. Not that it's going to be difficult to figure out, but did take me a few minutes to realize what was going on, heh. I just hope the auto parts store has the right part for me when I go to pick it up tomorrow...
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Was a royal pain in the ***, but I did get the old AOS out last night and am ready for the new. It's a significantly different part and a different procedure to attack, but still uses the same $^$%^#^ hose clamps as the older models' AOSs that quite literally took an hour of jimmying and two crowbars to finally persuade free. I at least didn't have to resort to the lead sledge!

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Done and running! Reinstall sure was easy, too. Got the auto parts store to clear the CEL, and I'd swear she's a bit peppier than last week :D I'll see at the autocross this weekend, I suppose.

04aos7.jpg

Curious what's in there, I grabbed a hammer and chisel and went to town! The base is hollow, in two separate (and isolated) chambers; there's nothing in there at all. You can peep through the nipples and see. The interesting bit is the diaphragm on top. Now, it looks like vacuum from the intake will pull the diaphragm shut upon start, but that high pressure from the crankcase will force it back open, allowing gasses to vent, but I'm unable to puzzle out how it excludes oil. Clearly, though, if it sticks open, the crankcase will be under vacuum, and oil will get sucked into the intake.

04aos8.jpg

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Grover:

Thanks for the follow up and explanation of how the AOS actually functions.

I notice a bit of greasy dirt around the junction of two of the parts of the oil fill tube. Maybe caused a small crack or the pieces not tightly fitted together, or maybe some left over from the failing AOS.

Regards, Maurice.

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Maurice, good eye, thanks, I'll check that out; and thanks to everyone who replied, I really appreciate the help! Props to Bap Geon, too, who got me a replacement AOS within 4 hours, and didn't complain when I realized I couldn't use the bellows I'd special ordered.

:thankyou:

Since I couldn't find any write-ups on the 03/04 Boxster AOS online or in the Bentley manual, I went ahead and posted an article in the DIY forum. Hopefully this will help someone:

http://www.renntech....04-boxster-aos/

Edited by grover
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