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The Wahler brand thermostat is a very popular replacement part for those of us who experience lower operating temperatures or leaks. Unfortunately, the Wahler thermostat has a weakness of its own. I have had two Wahler thermostats leak from the same area. That is the heating element interface with the thermostat. If it weren't for this design weakness, the Wahler would be perfect.

Here I will show you how to fix this issue with your Wahler thermostat using RTV.

The Wahler heating element is relatively easy to remove from the thermostat housing. It is held in with a relatively simple mechanism.

Simply lift this tab (I used an O-ring pick) and rotate the connector counter-clockwise.







Now you need to pry the heating element out of the thermostat housing. It's held in by friction at this point. I used a small flathead to leverage the connector body up and away from the housing.

This is the element removed. As you can see, the element is sealed using two O-rings. These O-rings are either incorrectly sized, a poor material, or installed poorly. I think it is a combination of the three. I will explain later.



This is the housing with the heating element removed.



This is an image of the smaller of the two O-rings. This is the primary seal. It's the first barrier for coolant from the inside of the housing. Notice how deformed it is? I believe it was installed with no assembly lubricant and rolled up unevenly on the element shaft. It was never able to do its job properly. I also believe this is a rather cheap material and probably doesn't have great heat aging properties. The primary reason for the poor sealing is the poor install, in my opinion.



So what can we do about this? The solution I have implemented is simply Red RTV.





Unfortunately, you can't just apply RTV all over the place and slide the element back into the housing. You will end up with RTV inside the thermostat itself and I don't know how that will affect the function. See below for what would end up in the thermostat.



You must first take off the thermostat. This was a simple task with some narrow jaw vise-grips. Needle nose pliers would probably also work. Just grip these tabs and push down and in. They'll pop out. It requires a decent bit of force. Do that for both sides.



Now you have this.



Now you can insert your element and clean it up. Twist and lock it into place as it was when you bought the termostat.





Now reinstall the thermostat. You have to push down both leg clips at the same time. I used two allen keys to press evenly on both legs until they clicked into place. If you bent them on removal, you will need to bend them back now so they'll clip into place.



Now you should have a permanently sealed thermostat. Wait at least 24 hours before installing this in your car (RTV cure time).
 

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I just installed a mahle with no issues. My OEM wahler was 12 years old and just started to leak around the outer housing seal
 

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My Wahler started leaking from that area and also what looks like around one of the mounting bolts, so I bought a Mahle/Behr tstat (going to put either Permatex Red rtv or The Right Stuff around the edges).
 

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Im done with Wahlers. Ive never had one leak at all but worse theyd make my car run too cool. Hopefully Behr thermostats are more thorough.
 

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Nice write up....I'll be keeping and eye on my Whaler tstat!
 

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Nice writeup and photos,i will remember to do this when my recently installed Wahler starts leaking.
If a thermostat needs to come off the motor just toss it and buy a new one.

Average lifespan is only about two years or 50k miles. Genuine BMW is the only way to go here.
 

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Discussion Starter #15
If a thermostat needs to come off the motor just toss it and buy a new one.

Average lifespan is only about two years or 50k miles. Genuine BMW is the only way to go here.
Agreed. I would probably only do this to a new thermostat before install. Not worth the effort otherwise.
 

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I am surprised the thermostat last long enough without going soft, triggering the P0128 or the other thermostat related codes before they actually leak.

Maybe for you guys in the warmer areas the stat may appear to last longer.

What I have found, over 70F will mask soft thermostats.

I just had to drive my daughters VW back 1100 miles with no cooling fans working. Not a problem, ambient temps never were above 60F and the only concern I has was for traffic back ups. When I came of slow traffic a few times, on when the HVAC fan full blast and the engine never got about 210F.

I had my UltraGauge on the car the entire trip with programmed temp alarms so I was not worried.

1100 straight thru stopping only for food, fuel and bathroom breaks. 70 MPH average speed for the entire 1100 miles. :thumbsup:
 

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This is an image of the smaller of the two O-rings. This is the primary seal. It's the first barrier for coolant from the inside of the housing. Notice how deformed it is? I believe it was installed with no assembly lubricant and rolled up unevenly on the element shaft. It was never able to do its job properly. I also believe this is a rather cheap material and probably doesn't have great heat aging properties. The primary reason for the poor sealing is the poor install, in my opinion.
I can appreciate your creativity here, but why not just replace the o-rings? A more durable o-ring installed correctly would be a cheap and simple safeguard.
 

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Discussion Starter #18 (Edited)
I am surprised the thermostat last long enough without going soft, triggering the P0128 or the other thermostat related codes before they actually leak.

Maybe for you guys in the warmer areas the stat may appear to last longer.

What I have found, over 70F will mask soft thermostats.

I just had to drive my daughters VW back 1100 miles with no cooling fans working. Not a problem, ambient temps never were above 60F and the only concern I has was for traffic back ups. When I came of slow traffic a few times, on when the HVAC fan full blast and the engine never got about 210F.

I had my UltraGauge on the car the entire trip with programmed temp alarms so I was not worried.

1100 straight thru stopping only for food, fuel and bathroom breaks. 70 MPH average speed for the entire 1100 miles. :thumbsup:
Mine is still good. The one in the car is 30-40K miles and was fine this winter when I was driving it. Always got up to 95C. It started leaking very early in its life.

I can appreciate your creativity here, but why not just replace the o-rings? A more durable o-ring installed correctly would be a cheap and simple safeguard.
Not much reason to spend more effort than just applying high temp RTV. It definitely will work and last. It's also very cheap.
 

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Thanks for the write up WDE46! Im glad it got bumped, i have a brand new whaler waiting for its day to get installed so I'll probably do this before its day comes:thumbsup:
 

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Hi WDE46,

Thanks for the pics and invaluable info.
I've gone through 2 leaky Wahler heating elements and it's annoying.

I don't have a new gasket on-hand, so don't want to remove the housing. Do you think the heating element could be removed with the housing still on the car? Then replace the o-rings or apply RTV and slide it back in.

Or is access to the back-side (therostat side) necessary?
 
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