09-11-2025, 11:05 AM
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#1
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Registered User
Join Date: Oct 2024
Location: San Jose, California
Posts: 121
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Does this rumbling noise sound like the idler pulleys?
I have a rumbling noise that occurs at idle most of the time, moreso when the car is cold. I managed to capture the noise in this video.
Before I order the 2 idler pulleys, am I on the right track here?
Thanks as always in advance!
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09-11-2025, 11:22 AM
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#2
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Registered User
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 6,639
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If you remove the belt, you can turn ALL the pulleys one at a time to see which one needs attention..............
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“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
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09-11-2025, 11:37 AM
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#3
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Registered User
Join Date: Oct 2024
Location: San Jose, California
Posts: 121
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Quote:
Originally Posted by JFP in PA
If you remove the belt, you can turn ALL the pulleys one at a time to see which one needs attention..............
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Ah great! Assume I'm looking to be able to recreate a noise of some description while turning them by hand?
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09-11-2025, 01:05 PM
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#4
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Registered User
Join Date: Feb 2005
Location: It's a kind of magic.....
Posts: 6,639
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Yes, a rumble or similar sound and feel.
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“Anything really new is invented only in one’s youth. Later, one becomes more experienced, more famous – and more stupid.” - Albert Einstein
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09-13-2025, 04:19 AM
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#5
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"50 Years of 550 Spyder"
Join Date: Jun 2015
Location: The Road
Posts: 961
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A bad idler pulley….
….is very bad news.
I have seen three different Boxsters go up in flames after an idler pulley failure.
Belt friction set that thing on fire.
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550 SE #310---"It's more fun to drive a slow car fast, than a fast car slow."
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09-14-2025, 01:09 PM
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#6
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Registered User
Join Date: Oct 2024
Location: San Jose, California
Posts: 121
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Quote:
Originally Posted by 10/10ths
….is very bad news.
I have seen three different Boxsters go up in flames after an idler pulley failure.
Belt friction set that thing on fire.
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I got access to it today while I'm waiting for time to take the belt off. I can hear the noise much better with the access panel off.
Can someone take a look at this latest video that shows the rumble a lot better and let me know if I'm on the right track with the pulleys, or is this loud enough that it could be something else?
Regardless I'll be taking the belt off to check the pulley bearings as @JFP in PA mentioned, but wanted to check in case this is something else that I would need parts for so I can get them ordered.
Last edited by BoxsterInTheSun; 09-14-2025 at 01:12 PM.
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09-14-2025, 08:55 PM
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#7
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Registered User
Join Date: Jul 2024
Location: Western Europe
Posts: 220
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I also think it is one of the bearings of one of the pulleys. Take the opportunity to renew the belt as well. If the AC compressor might be the culprit, switch it on and off and check the difference -- if there is any.
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09-15-2025, 02:49 AM
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#8
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Registered Member
Join Date: Oct 2022
Location: NJ
Posts: 203
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With all due respect, taking the belt off is about a 30 second operation. Just do it.
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Tom Coradeschi
03 Boxster
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09-16-2025, 06:33 PM
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#9
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Registered User
Join Date: Oct 2024
Location: San Jose, California
Posts: 121
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Quote:
Originally Posted by tcoradeschi
With all due respect, taking the belt off is about a 30 second operation. Just do it.
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Got the belt off tonight and took a look. I'm not completely sure what I'm looking for to know if the pulleys are "bad" or not. I took a video of me rolling them, would anyone mind taking a look and letting me know how they seem?
I'm not sure that anything I'm hearing here would equate to the noise I hear in the original video I posted, but maybe that's all it takes?
Thanks as always for the help!
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09-16-2025, 08:01 PM
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#10
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Registered User
Join Date: Jul 2019
Location: Finland
Posts: 349
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Quote:
Originally Posted by BoxsterInTheSun
Got the belt off tonight and took a look. I'm not completely sure what I'm looking for to know if the pulleys are "bad" or not. I took a video of me rolling them, would anyone mind taking a look and letting me know how they seem?
I'm not sure that anything I'm hearing here would equate to the noise I hear in the original video I posted, but maybe that's all it takes?
Thanks as always for the help! |
That bearing you rotate by hand is gone. Should be basically silent when it is good.
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2001 996 C2 Manual
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09-16-2025, 08:06 PM
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#11
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Registered User
Join Date: Oct 2024
Location: San Jose, California
Posts: 121
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Quote:
Originally Posted by pilot4fn
That bearing you rotate by hand is gone. Should be basically silent when it is good.
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Thank you so much! So the first and second ones in the video ( the upper and lower idler pulleys )? The tensionser pulley doesn't seem to make noise.
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09-16-2025, 10:19 PM
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#12
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Registered User
Join Date: Jul 2024
Location: Western Europe
Posts: 220
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You identified them by yourself: "noisy".
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09-17-2025, 09:08 AM
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#13
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Registered User
Join Date: Oct 2024
Location: San Jose, California
Posts: 121
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Quote:
Originally Posted by 997_986
You identified them by yourself: "noisy".
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I have just ordered replacements for the first two ( upper and lower idler pulleys ), I figure I might as well just replace them anyway. The tensioner pulley seems "stiff" to me, but isn't noisy at all, maybe that's how it's supposed to be?
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09-17-2025, 09:54 PM
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#14
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Registered User
Join Date: Jul 2024
Location: Western Europe
Posts: 220
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Correct, if it's not running rough or noisy it should be fine. And do not forget to engage the clutch of the AC-compressor to rule that bearing out.
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09-18-2025, 07:27 AM
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#15
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Registered User
Join Date: Jan 2019
Location: PA
Posts: 1,726
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Quote:
Originally Posted by BoxsterInTheSun
Got the belt off tonight and took a look. I'm not completely sure what I'm looking for to know if the pulleys are "bad" or not. I took a video of me rolling them, would anyone mind taking a look and letting me know how they seem?
I'm not sure that anything I'm hearing here would equate to the noise I hear in the original video I posted, but maybe that's all it takes?
Thanks as always for the help! |
Looks and sounds to me like the first two you spun need replaced. The first one may be louder and definitely the one causing most of your noise, but the second one isn't far behind. When it spins freely like that, it means that the grease is gone. The third one is quiet, and quickly stops, which means it still has grease.
__________________
2002 Boxster Base - Arctic Silver - Tiptronic
2010 Subaru Forester
1980 Ford C-8000 Custom Cab Emergency-One Fire Truck
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"I never lose. I either win or I learn." -Nelson Mandela
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Today, 04:47 AM
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#16
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Toppy
Join Date: Apr 2014
Location: Dorchester, ON, Canada
Posts: 143
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Any opinion on just replacing the bearings, instead of the complete assembly
__________________
1999 Boxster
Arena Red/Graphite Grey Interior/Black 03 Top/550 All Red Tail Lights
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Today, 10:18 AM
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#17
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1998 Boxster Silver/Red
Join Date: Sep 2017
Location: 92262
Posts: 3,091
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Pull the respective pulley... pop off the plastic retaining ring... examine the bearings... bad? Replace with new bearings... press in some grease (by hand) reinstall the plastic retaining ring... reinstall the pulley.
Bearings good, upon inspection? Remove the bearings... spray clean the bearings and the pulley... reinstall the bearings... regrease... reinstall the ring... close it up and reinstall the pulley.
Go driving. 
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1998 Porsche Boxster
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