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2005 330xi Auto, 2006 330ci Vert Auto
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Discussion Starter · #1 ·
I want to pass along some recent experiences with Wahler thermostats. Wahler thermostats have been well-regarded as a good replacement for E46. I have 2 E46 and I replaced the thermostat on E46#1 with a Wahler in Sept 2021 shortly after purchasing the car as preventative maintenance since I can see caked coolant on the bottom side of the thermostat. In addition, I replaced the thermostat on E46#2 with a Wahler in June 2022 as preventative maintenance since I was replacing a leaky water pump.

In Nov 2022, about 5 months after I installed the Wahler on E46#2, I noticed that coolant was leaking from the bottom of the thermostat. Upon investigation, I determined the thermostat wasn't sealing properly against the engine block. I replaced it with FCP's lifetime warranty with another Wahler. I installed the replacement and so far it's fine. It cost me a couple of hours of time, new coolant, and return shipping to FCP.

After this, I naturally went to check on E46#1 and I noticed that coolant has been leaking for a while from the bottom of the thermostat, just like my E46#2. The leak was small enough that coolant only got as far as the bottom splash guard and around the front of the engine. Coolant never got on the ground so I never noticed. The leak was small enough that I never lost significant coolant. Upon investigation, once again I determined the thermostat wasn't sealing properly against the engine block. Now I was alarmed that both Wahlers have failed the same way. This time with my E46#1, I didn't want to just install another Wahler in case there was an inherent defect such that I would have to replace it over and over again every 6 months.

Since the leak was a bad seal against the engine block, I elected to buy replacement thermostat gaskets instead of doing a warranty replacement with FCP Euro. I purchased a BMW one (~$10) and an Elring (~$6). I removed the gasket from the leaking Wahler thermostat from E46#1 and compared it to the replacement gaskets I purchased. The leaking one is on the left and the new BMW one is on the right. They look almost the same, but when I put a caliper to them, there is what I measured:

Old leaking one from Wahler - 0.210" (width)
New BMW one - 0.235" (width)
New Elring one - 0.232" (width)

Red Wood Wrist Rope Thumb


So there's a (possibly significant) difference between the Wahler gasket vs. BMW and Elring. It should be noted that the leaking Wahler gasket had been used (compressed) for ~12-14 months so that may affect its physical measurement.

Rather than returning the Wahler to FCP Euro for a warranty replacement, I elected to simply replace the gasket with a BMW one. It's been a couple of days and so far so good. This cost me a couple of hours of time, new coolant, and ~$10 for the new gasket.

I hope this data helps some of you to draw your own conclusion.
 

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04 325XIT 05 325IT 03 325XI 05 X5 3.0
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I want to pass along some recent experiences with Wahler thermostats. Wahler thermostats have been well-regarded as a good replacement for E46. I have 2 E46 and I replaced the thermostat on E46#1 with a Wahler in Sept 2021 shortly after purchasing the car as preventative maintenance since I can see caked coolant on the bottom side of the thermostat. In addition, I replaced the thermostat on E46#2 with a Wahler in June 2022 as preventative maintenance since I was replacing a leaky water pump.

In Nov 2022, about 5 months after I installed the Wahler on E46#2, I noticed that coolant was leaking from the bottom of the thermostat. Upon investigation, I determined the thermostat wasn't sealing properly against the engine block. I replaced it with FCP's lifetime warranty with another Wahler. I installed the replacement and so far it's fine. It cost me a couple of hours of time, new coolant, and return shipping to FCP.

After this, I naturally went to check on E46#1 and I noticed that coolant has been leaking for a while from the bottom of the thermostat, just like my E46#2. The leak was small enough that coolant only got as far as the bottom splash guard and around the front of the engine. Coolant never got on the ground so I never noticed. The leak was small enough that I never lost significant coolant. Upon investigation, once again I determined the thermostat wasn't sealing properly against the engine block. Now I was alarmed that both Wahlers have failed the same way. This time with my E46#1, I didn't want to just install another Wahler in case there was an inherent defect such that I would have to replace it over and over again every 6 months.

Since the leak was a bad seal against the engine block, I elected to buy replacement thermostat gaskets instead of doing a warranty replacement with FCP Euro. I purchased a BMW one (~$10) and an Elring (~$6). I removed the gasket from the leaking Wahler thermostat from E46#1 and compared it to the replacement gaskets I purchased. The leaking one is on the left and the new BMW one is on the right. They look almost the same, but when I put a caliper to them, there is what I measured:

Old leaking one from Wahler - 0.210" (width)
New BMW one - 0.235" (width)
New Elring one - 0.232" (width)

View attachment 966796

So there's a (possibly significant) difference between the Wahler gasket vs. BMW and Elring. It should be noted that the leaking Wahler gasket had been used (compressed) for ~12-14 months so that may affect its physical measurement.

Rather than returning the Wahler to FCP Euro for a warranty replacement, I elected to simply replace the gasket with a BMW one. It's been a couple of days and so far so good. This cost me a couple of hours of time, new coolant, and ~$10 for the new gasket.

I hope this data helps some of you to draw your own conclusion.
Thank you for this - as a reference I have replaced 3 M54, 1 in 11/2018 and 2 around 5/2020 with FCP Wahlers for a P0599( thermostat circuit high something).
They have not been leaking...
Batch Quality control issue???
 

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Е46 sedan M52B20TU 1999
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231 Posts
Thanks for the info!
I choose between wahler and mahle / behr ... while studying people's reviews, I noticed that many complain about the wahler leaking after about six months, as well as leaking from under the connector on top of the thermostat ... but I think this is solved by replacing the seals. I have not seen mahle/behr leaks. My e46 has vernet calorstat 97" but it seems to me that it works badly, because at idle the temperature reaches 102's ... but there is no leak. It is from the previous owner, more than 3 years old, no leaks.
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2000 323i
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My experience with wahler isn’t good. I bought mine, installed it. It started to leak from the heater core O-rings. So I used the RTV trick and new O-rings but it also leaked after some time. The whole front of the T-stat is covered with gunk. I have to add about 100ml of coolant after 5000kms which is nothing significant but I like my engine bay clean and that is my concern with Wahler. I ordered new gasket for it and I will see if the original one was faulty. We also tried new Behr T-stat for my friends E46 and so far it looks good. It’s a single piece design without O-rings around heater core. I like it better. My Wahler also started to kind of soft-fail, because when there is colder outside and I give it a more gas on the highway the temperature gauge needle drops by a good amount which I think is intolerable.
 

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2003 325i Touring
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5,422 Posts
I'm sorry, but comparing a used o-ring/seal to new o-rings/seals is not a valid comparison. The used o-ring/seal has been compressed and has endured numerous heat cycles and simply will not still be the same as it was new.

My issues with Wahler t-stats have always been weepage around the heating element. Went genuine on the replacement for the last weepy Wahler. I've never had one leak from the seal to the engine. Since it happened more than once, you may need to revisit your surface prep and torqueing procedure.
 

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I had the leaking at the heating element on one and also found that as i also had coded the temp gauge to be more accurate that the needle jumped around in an alarming way,so much that a week later i fitted some othe brand -which i forget but that it now behaves its self.
 

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2005 330xi Auto, 2006 330ci Vert Auto
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Discussion Starter · #8 ·
Thank you for this - as a reference I have replaced 3 M54, 1 in 11/2018 and 2 around 5/2020 with FCP Wahlers for a P0599( thermostat circuit high something).
They have not been leaking...
Batch Quality control issue???
I'm also thinking batch QC problem on the gasket. The thermostat itself works just fine, but in my case the gasket(s) was problematic.
 

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2005 330xi Auto, 2006 330ci Vert Auto
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Discussion Starter · #9 ·
I'm sorry, but comparing a used o-ring/seal to new o-rings/seals is not a valid comparison. The used o-ring/seal has been compressed and has endured numerous heat cycles and simply will not still be the same as it was new.

My issues with Wahler t-stats have always been weepage around the heating element. Went genuine on the replacement for the last weepy Wahler. I've never had one leak from the seal to the engine. Since it happened more than once, you may need to revisit your surface prep and torqueing procedure.
I agree that comparing used o-ring vs. new has some caveats. At the same time, do you expect significant changes after 3 months and a couple of thousand miles (I don't drive much post-Covid)? I'll let the readers decide for themselves. They are supposed to last many years and many 10's of thousands of miles, right? As I noted in my post, I wanted to post some data so the readers can form their own opinions.

I'm positive my surface prep and torque procedure are good :) . For example, this is what it looked like after surface prep and just before installation on E46#2 in June 2022. Torque specs per Bentley manual and per the torque guides (Archbid) available on this forum. I used Techton 1/4" and 3/8" torque wrenches.

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Thanks for this.

My historical experience with Wahler has been that their
QC isn't great (leaking M10 thermostats from day 1)
but that their durability is excellent if you get a good one.

I have been VERY unimpressed with everything else that wasn't BMW.
So I've recently installed a Wahler. I need to change another hose on that car
(no thanks to Febi- their lower hose doesn't fit) so I'll swap the t- stat gasket while
the thing's drained. And see if mine was leaking as well.

t
 

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I agree that comparing used o-ring vs. new has some caveats. At the same time, do you expect significant changes after 3 months and a couple of thousand miles (I don't drive much post-Covid)? I'll let the readers decide for themselves. They are supposed to last many years and many 10's of thousands of miles, right? As I noted in my post, I wanted to post some data so the readers can form their own opinions.

I'm positive my surface prep and torque procedure are good :) . For example, this is what it looked like after surface prep and just before installation on E46#2 in June 2022. Torque specs per Bentley manual and per the torque guides (Archbid) available on this forum. I used Techton 1/4" and 3/8" torque wrenches.

View attachment 966816
Wow that is one awesome surface prep!!! I could eat off that surface-😀anyway I clean and run my fingers on the surface if its smooth to touch I Would call it a day and finish the install .I don't even torque the bolts and doubt any BMW technician in a dealership even torque it...as of today no leaks.
With regards to the gasket .my opinion is it shouldn't be deformed at 3 months of service - it should be able to revert back to its original form at 3 months.
 

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2005 330xi Auto, 2006 330ci Vert Auto
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Discussion Starter · #15 ·
Besides my limited (2 data points) experience with the gasket as described in this post, so far the Wahler is functionally very reliable for me. It has been working very well regulating the coolant temperature and I'm seeing operating temperatures of 93-95C. I'm hoping that the gasket issue is simply a QC issue. I'm guessing here a bit, but I suspect Wahler doesn't make their own gaskets but rather source them from someone else. Personally, I would still buy Wahler, but I would check the gasket prior to installation.
 

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2004 325xi, 2000 323ci, 2012 135i
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65 Posts
About 7 years ago I bought a Stant Thermostat on sale from Advance Auto which was actually just a reboxed Wahler. I stored it in garage in case mine ever failed or started.

I replaced it roughly two years ago after it started soft-failing on my M54, the fitment was perfect with no leaks. I wonder if its a quality deficiency on the newer manufactured Wahler Tstats.
 
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