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Discussion Starter #1 (Edited)
Long time member, first time poster. Been searching for 2 weeks and finally decided to post.

So I've got SES code P0128, which I strongly suspect is the thermostat. However, my car is also starting to make a clunking noise and my question is are the two related?

The noise kicks in only once the car is fully warmed up when I'm slowing down and is heard form 30mph down to 20mph and then ultimately stops. The noise does not happen at any speeds, or high speeds. It can be described as a "thunk thunk thunk thunk" sound all the way from 30mph to 20mph, regardless of in gear or neutral.

Is anyone familiar with this and are the two related?

I'm fixing the thermostat, but would love to get to the bottom of the noise too. Any help is deeply appreciated.

Cheers!
 

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I have no idea what the noise could be, but I can think of only one noise that could cause your code. If the water pump was failing it may not make a noise until the T-Stat opened and it may some how prevent the car warming up in the correct way, which causes the code. I think you would have other symptoms. It would also not likely only happen between 20 - 30.
On that note I would say the two are not likely connected which was what you were asking.
 

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Discussion Starter #3
Thanks for your timely response.

What further frustrates me is that it only happens between 30-20mph, specifically when slowing down from 30 to 20. This specific range leads me to believe that it isn't anything loose, but I'm not crossing that out yet.

Any other feedback is appreciated. Thanks in advance.
 

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Discussion Starter #4
Going to reference this thread (as it's the only one I can find about rattling thermostats): Rattling noise in pump or thermostat...

atlantisvip said:
The impeller in your water pump could have broken and the pieces are flying around.. Not sure about the 5s but E36s had an issue with faulty plastic impellers.


waterboy said:
I had a 92 525i and mine would make that sound but not so much as what you said but mine was from the thermostat it has just a little play in it
 

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We have metal impellers, and a 92 525 not some thing that is a good example, totally different. I have one of those still a wagon.
If you want to rule out the pump take of the BELT AND DO A VERY SHORT DRIVE AND SEE IF THE SOUND GOES.
 

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It's not related to the P0128 code, IMO. It's drivetrain related since you hear it with the clutch in or out when slowing down. So a u-joint or CV-joint maybe.
 

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Discussion Starter #7
It's not related to the P0128 code, IMO. It's drivetrain related since you hear it with the clutch in or out when slowing down. So a u-joint or CV-joint maybe.
Thank you. I knew it would be a stretch if the two were related.

Fixing the thermostat this weekend so I'll have updates after.
 

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Discussion Starter #10
Thermostat is fixed, but still hearing this clunking noise once the car is fully warmed up.

Repeating clunking noise that sounds like it's coming from the front driver wheel area around 20-40mph.

Only happens when the car is fully warmed (20 minutes of driving), any ideas?
 

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Discussion Starter #11
Believe it or not the noise was associated with the Thermostat. Thermostat now has 1,000 miles and the noises are no longer here. Hopefully this helps someone.
 

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Can you throw the old one in a pot of water?? Sitting static is it open? Heat it in water at what water temp do you see it open? At 85C pull it out and measure how far it is open.
I believe you there was noise , I just want to figure out why. You asked for help now we need your help to add to the knowledge.
 

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I would suggest that clunking could be centre link and or tie rods, classic symptoms of it, and it can disappear and come back, seems temperature related and also if carrying a front passenger or not. I have an iphone clip of mine doing that at low speed, clunking real bad before replacing those items.
 
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