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The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 10-08-2019, 03:18 PM
McLarenBMW McLarenBMW is offline
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Magnitude of the P0128 code?

How serious is this coolant thermostat code and how quickly should I replace it?
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  #2  
Old 10-08-2019, 08:40 PM
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Originally Posted by McLarenBMW View Post
How serious is this coolant thermostat code and how quickly should I replace it?
Your tstat has “soft failed” in the open position. You wont reach full operating temp affecting fuel economy and likely wont get heat when it is really cold out. Beyond that, not super urgent but I wouldnt play around waiting too long. Cooling system issues and these engines are a potentially lethal (to your engine) problem.
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Old 10-08-2019, 08:54 PM
McLarenBMW McLarenBMW is offline
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Originally Posted by McLarenBMW View Post
How serious is this coolant thermostat code and how quickly should I replace it?
Your tstat has "soft failed" in the open position. You wont reach full operating temp affecting fuel economy and likely wont get heat when it is really cold out. Beyond that, not super urgent but I wouldnt play around waiting too long. Cooling system issues and these engines are a potentially lethal (to your engine) problem.
Thanks, my car still reaches optimal temp but it takes a while for the needle to get to the middle
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Old 10-08-2019, 08:57 PM
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Thanks, my car still reaches optimal temp but it takes a while for the needle to get to the middle
Keep in mind, “middle” on the gauge can be anywhere from 160 degrees F to 225 or so, it is heavily buffered. If it was really cold outside, I bet the gauge stays left of center. They dont usually fail closed (causing an overheat) once they have failed open, but again, replacing it is cheap and easy, I wouldnt wait too long.
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Old 10-09-2019, 10:14 AM
McLarenBMW McLarenBMW is offline
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Thanks, my car still reaches optimal temp but it takes a while for the needle to get to the middle
Keep in mind, "middle" on the gauge can be anywhere from 160 degrees F to 225 or so, it is heavily buffered. If it was really cold outside, I bet the gauge stays left of center. They dont usually fail closed (causing an overheat) once they have failed open, but again, replacing it is cheap and easy, I wouldnt wait too long.
You don't absolutely need to get a Wahler one, right? Aftermarket works too?
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Old 10-09-2019, 10:23 AM
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Doug Huffman Doug Huffman is offline
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They dont usually fail closed (causing an overheat) once they have failed open,
I wonder why that is. Opening is by a wax-pellet linear motor that is more powerful than the shutting spring, itself quite powerful. When the engine is shut off and cools, the wax-pellet motor loses power and the spring becomes more powerful than the deenergized wax-pellet motor and shuts the thermostatic valve.

It's too bad that no one reliable has collected failure mode statistics.
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Last edited by Doug Huffman; 10-09-2019 at 10:25 AM.
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Old 10-09-2019, 01:17 PM
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smolck smolck is offline
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I wonder why that is. Opening is by a wax-pellet linear motor that is more powerful than the shutting spring, itself quite powerful. When the engine is shut off and cools, the wax-pellet motor loses power and the spring becomes more powerful than the deenergized wax-pellet motor and shuts the thermostatic valve.

It's too bad that no one reliable has collected failure mode statistics.
I have them fail closed and open on many cars. I didnt collect the data.
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Old 10-09-2019, 01:18 PM
McLarenBMW McLarenBMW is offline
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I wonder why that is. Opening is by a wax-pellet linear motor that is more powerful than the shutting spring, itself quite powerful. When the engine is shut off and cools, the wax-pellet motor loses power and the spring becomes more powerful than the deenergized wax-pellet motor and shuts the thermostatic valve.

It's too bad that no one reliable has collected failure mode statistics.
I have them fail closed and open on many cars. I didnt collect the data.
Can someone confirm if a Wahler is absolutely necessary or does aftermarket brand work as well?
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Old 10-09-2019, 01:21 PM
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smolck smolck is offline
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Can someone confirm if a Wahler is absolutely necessary or does aftermarket brand work as well?
I’d go with Mahle, FCP has them on sale for $45 and a lifetime warranty. How can you lose? But Wahler works too, but dont cheap out and buy chinese garbage, not worth it.
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now, go burn your Man Card, and buy yourself a Camry....
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  #10  
Old 10-09-2019, 01:24 PM
McLarenBMW McLarenBMW is offline
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Originally Posted by McLarenBMW View Post
Can someone confirm if a Wahler is absolutely necessary or does aftermarket brand work as well?
I'd go with Mahle, FCP has them on sale for $45 and a lifetime warranty. How can you lose? But Wahler works too, but dont cheap out and buy chinese garbage, not worth it.
I'm Canadian, that Mahle is 80 bucks here. I got an aftermarket one on Amazon from Kimiss (whoever tf they are) and it looks high quality. Also not Chinese

Last edited by McLarenBMW; 10-09-2019 at 01:26 PM.
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Old 10-09-2019, 07:58 PM
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I'm Canadian, that Mahle is 80 bucks here. I got an aftermarket one on Amazon from Kimiss (whoever tf they are) and it looks high quality. Also not Chinese
never heard of it. $80 for a proper thermostat is not bad. Taking chances with your cooling system is ill advised. Good luck
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Old 10-09-2019, 08:17 PM
BabyUnicornTaco BabyUnicornTaco is offline
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Get the proper thermostat. Mahle is the choice.


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