OEM composite thermostat housing on my 97 528 is leaking yet again

[BMW540san]

First of all I've read endless debates about composite vs aluminum housing. It's obvious that most aluminum hosuings are inferior quality but composite material has its weaknesses too.

The OEM housing that I've installed about 5 years ago developed the tiny crack and after a lot of consideration, I've gone with another OEM housing, o ring and water outlet gasket, all purchased from dealer.

This was about 6 months ago and while I'm aware that's under warranty, I've had enough with OEM. This time there is a slow leak just above the WP area and it's almost impossible to see until you use a mirror and there is slight residue on belt underneath.

When I installed the current housing, I've done the following:

Thoroughly cleaned the surface of the head
10NM torque in slow sequences while making sure to use star pattern between the bolts to create even pressure
Made sure that everything was seated properly and there was no leaks for 6 months

Whatever it is this time, I don't care, here is a new course of action:

Beck Arnley housing, made in USA. I suspect it's rebrand but it looks decent quality. Also, it came with red gasket included but it's plainly to thick and not sure about the quality.
Victor Reinz o ring and gasket, made in Germany
Permatex thermostat housing rtv

While I understand that o ring and gasket are negating the need of rtv, there is achance that aluminum housing may not seat 100% against head and therefore I'll use very small amount of rtv to make up for it. We'll see what happens.

Bottom line is this: Even though it's a very slow leak, it'd be stupid just to leave it and not to mention that system is not fully pressurized, plus belts don't like antifreeze.

I don't have to worry about the aluminum housing cracking and we'll see how it's going to seal.

[philly98540]

Sorry to hear about your leak (again). What a pain. I'm sure your install was done right. It just seems the you can not depend on parts that are being made these days. We are seeing parts issues at my work all the time now. Sucz.

Looks like you got a great solution in plan there. You are now the resident t-stat expert!!

[Mannyf540]

You got that at Beck Arnely? Nice observations, my housing is aluminum but I thought that was oem ? I see Zionsville has aluminum housings as well.

[BMW540san]

Sorry to hear about your leak (again). What a pain. I'm sure your install was done right. It just seems the you can not depend on parts that are being made these days. We are seeing parts issues at my work all the time now. Sucz.

Looks like you got a great solution in plan there. You are now the resident t-stat expert!!

You're giving me to much credit because I haven't installed it yet. Even with rtv, it still may leak. I'm trying to rack my brain if somehow I'm not installing the composite housing correctly but I'm following all the procedures and then some. Somebody has to be guinea pig with this brand and rtv combination. I wonder if the OEM composite housing is lower quality than it use to be.

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You got that at Beck Arnely? Nice observations, my housing is aluminum but I thought that was oem ? I see Zionsville has aluminum housings as well.

You're not confusing this with 540, are you. OEM thermostat on M52, M52TU or M54 was always composite, although the integrated unit on M52TU and M54 seems to be less leak prone.
I'm not putting to much faith in Beck Arnley other than nice to see it's made in USA. It's only $16+ shipping at RockAuto so I'm sure it's not really high end aluminum cast. I suspect it's rebrand because Beck Arnley has been known to do that.

[Mannyf540]

Yeah my bad, I thought you were referring to the 540 v8.

[JimLev]

On waterpump gaskets or any that see coolant Permatex makes an RTV for this application, it's p/n 22071.

http://shop.advanceautoparts.com/web...atex_7160009-p

[BMW540san]

On waterpump gaskets or any that see coolant Permatex make an RTV for this application, it's p/n 22071.

http://shop.advanceautoparts.com/web...atex_7160009-p

Yes, that's the one in the picture. I've used the thin layer behind WP (not the WP but the water outlet) when I've done TC guides on 540. I'll get the fresh one today to play it safe. The one in picture has been open for a while now.

[cnn]

The OEM Plastic Housing should last some 80K.
The leak is from the seal, happened to me after 30K, replaced the red seal (but kept the 30K-old plastic tstat housing) and all is fine now.

The aluminum issue is from straightness.
Just get very fine sand paper (like 1000 grit), place the sand paper on a nice flat surface.
Then slide the Al housing back and forth until it is shiny and smooth, i.e., perfectly straight.

[wile87]

I always use a thinbead of rtv just outside the ring gasket. No more leaks from therm or w-p.

[BMW540san]

The OEM Plastic Housing should last some 80K.
The leak is from the seal, happened to me after 30K, replaced the red seal (but kept the 30K-old plastic tstat housing) and all is fine now.

The aluminum issue is from straightness.
Just get very fine sand paper (like 1000 grit), place the sand paper on a nice flat surface.
Then slide the Al housing back and forth until it is shiny and smooth, i.e., perfectly straight.

I'll check the seal when I remove it but I'm done with composite. I'm yet to check the straightness on aluminum, good idea. Even if the seal fails on aluminum housing, the rtv should stop it from leaking outside and I'm not seeing aluminum developing cracks like the composite. for the longevity of the actual material, aluminum is way to go unless is a terrible cast quality.

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I always use a thinbead of rtv just outside the ring gasket. No more leaks from therm or w-p.

I was trying to avoid using rtv on composite material since I believe the composite is not really compatible with rtv? Either way, if I can eliminate one more composite piece out of the engine bay, I'll do it.

[Stück]

Beck/Arnley are just repackagers. Thats the standard APA/URO made thermostat housing, and it isn't made in USA I'll promise you that. There is nothing wrong with that housing, but I always flat out the mating surface as described above, and clean up the casting flash in the passages with a carbine bit on a die grinder.

NO RTV should be used on the housing. Period.

If you bought the OE parts at the dealer bring the car there. The parts warrant includes having a dealer tech R&R the failed components.

[16valex]

Ha ha! Finally someone else has experienced the same agony after three freaking thermostat housing in 2 years I went with aluminum housing, Victor Reinz gasket and Permatex RTV.

Yeah! Don't bother with the Beck's gasket..Way to thick.
Do what Cnn said about the mating surface.
Lastly, let it sits overnight before refilling coolant.
No leaks yet for me...

[BMW540san]

Beck/Arnley are just repackagers. Thats the standard APA/URO made thermostat housing, and it isn't made in USA I'll promise you that. There is nothing wrong with that housing, but I always flat out the mating surface as described above, and clean up the casting flash in the passages with a carbine bit on a die grinder.

NO RTV should be used on the housing. Period.

If you bought the OE parts at the dealer bring the car there. The parts warrant includes having a dealer tech R&R the failed components.

To be honest, I've held URO housing in my hands and this one feels and looks better made. Beck Arnley is enough reputable brand that I doubt they would lie where it's made.

I'd have to disagree on rtv. I'd use very slim coating of proper rtv on outer edges where metal meets metal. I went 100% by the book and it still leaked.

I thought I bought it at dealer but then I checked my records and its rmeuropean. For $28 it's not even worth the hassle and packing and paying for the shipping back to them. I didn't know that fact about the dealer. To be honest, I'd rather replace it myself. Dealer service is not in high regard in my book.

You're right about making sure surfaces are flat and I did notice some rough casting inside, good tip.

Don't take this the wrong way, but I'm curious on what facts are you basing your statements about the Beck Arnley and rtv.

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Ha ha! Finally someone else has experienced the same agony after three freaking thermostat housing in 2 years I went with aluminum housing, Victor Reinz gasket and Permatex RTV.

Yeah! Don't bother with the Beck's gasket..Way to thick.
Do what Cnn said about the mating surface.
Lastly, let it sits overnight before refilling coolant.
No leaks yet for me...

Thank you. Now I feel less insane although not completely right, lol. I'm glad to see that it's paying off in your case. Thanks for the advice.

[Stück]

Don't take this the wrong way, but I'm curious on what facts are you basing your statements about the Beck Arnley and rtv.

Beck and Arnley are importers, and manupackagers. They slap other companies products in their own packaging for resale. Thats what they do, and that is nothing new in the automotive industry. APA/URO and RONAK are the two major suppliers of replica thermostat housings cast in aluminum. That one pictured is one of them.

That seal does not call for any RTV in the TIS procedure. I hate RTV, be it small or large amounts, put in places it doesn't belong. Its my favorite calling card of hack mechanics.

The oring and profile gasket will seal near-indefinitely if the mating surfaces are properly cleaned and prepared, something most people simply do not do.

The ONLY time I would EVER use RTV on either of those seals is if the cylinder head casting at the sealing point(s) is badly pitted from corrosion caused years of operation with straight tap water, and only as a stop gap to try to get a seal on a compromised mating surface.

I also stopped using Victor Reinz a long time ago. Their sealing products are sub par across the board for almost all the BMW's I work on. Elring is the OE supplier for most of the M5x engine seal products, stick with them whenever possible and you'll have a better ownership experience.

[cnn]

Aluminum has another issue: crack, not often but it does happen.
Just google "e39 aluminum thermostat housing crack" and you will see the threads.

I understand BMW plastic housing is not perfect, but I am using it and replace it every 80K or so.
Someone told me you can use E46 BMW aluminum housing, but you will have to modify the rad hoses.

[BMW540san]

Beck and Arnley are importers, and manupackagers. They slap other companies products in their own packaging for resale. Thats what they do, and that is nothing new in the automotive industry. APA/URO and RONAK are the two major suppliers of replica thermostat housings cast in aluminum. That one pictured is one of them.

That seal does not call for any RTV in the TIS procedure. I hate RTV, be it small or large amounts, put in places it doesn't belong. Its my favorite calling card of hack mechanics.

The oring and profile gasket will seal near-indefinitely if the mating surfaces are properly cleaned and prepared, something most people simply do not do.

The ONLY time I would EVER use RTV on either of those seals is if the cylinder head casting at the sealing point(s) is badly pitted from corrosion caused years of operation with straight tap water, and only as a stop gap to try to get a seal on a compromised mating surface.

I also stopped using Victor Reinz a long time ago. Their sealing products are sub par across the board for almost all the BMW's I work on. Elring is the OE supplier for most of the M5x engine seal products, stick with them whenever possible and you'll have a better ownership experience.

Thank you for your response. The reason I went this route is exactly because I followed the advice you're providing, which is sound: follow tis, Bentley, proper torque with calibrated torque wrench, clean all surfaces and it still leaked.

I've had this for 11 years now and 540 for 10 and everything I've done was always done following the right procedures. Am I master mechanic, no, but I'm skilled enough to know that in this case something isn't working. It's also proven that Bentley and TIS aren't always the best way. There are "factory trained technician" who route the belt the wrong way.

While I agree with you that TH isn't designed to be used with rtv, I'll try it and see what happens. if I'm wrong, I'll admit it. Your opinion is well appreciated and considered.

- - - Updated - - -

Aluminum has another issue: crack, not often but it does happen.
Just google "e39 aluminum thermostat housing crack" and you will see the threads.

I understand BMW plastic housing is not perfect, but I am using it and replace it every 80K or so.
Someone told me you can use E46 BMW aluminum housing, but you will have to modify the rad hoses.

You're right, there are cases of cracking although less than plastic. I suspect if the cast is decent quality, cracking should not be an issue. I've checked the surface earlier against the other smooth surface and it's perfect. I'll try it and report.

[16valex]

540san,
I would hire you to work on my car, your thoughts are sound. You're going to be OK.

[achtung98m]

540san,
Can you please provide an update? (hopefully the response is - "so far so good, no leaks!")
I am mid-way through my cooling system refresh project and now getting ready to put on the thermostat parts. I wasnt planning on applying RTV but read your post and seems to be logical. The way I'm thinking about it is that although applying RTV to the Tstat housing may be like "belt and suspenders" to other members, I'm just thinking(hoping) it would rather apply some RTV rather than re-do. How did the permatex product you used work out for you? How thin of a bead, similar to the attached pic or less? (pic taken from another thread

http://forums.bimmerforums.com/forum...nal-RTV-or-not

- I was thinking that as long as there is sealant that squeezes out after tightening then I've applied enough) I'm thinking the RTV is probably paper thin when the bolts are fully tightened and torqued.

- Speaking of torque, bentley says 7ft lbs (= 10nms), I was thinking this was info given out there so not to risk cracking OE composite housing, would an aluminum housing require (and withstand) more torque?

- Also, after applying the RTV on the housing did you immediately attach and tighten to torque specs or did you wait some time?

[BMW540san]

540san,
Can you please provide an update? (hopefully the response is - "so far so good, no leaks!")
I am mid-way through my cooling system refresh project and now getting ready to put on the thermostat parts. I wasnt planning on applying RTV but read your post and seems to be logical. The way I'm thinking about it is that although applying RTV to the Tstat housing may be like "belt and suspenders" to other members, I'm just thinking(hoping) it would rather apply some RTV rather than re-do. How did the permatex product you used work out for you? How thin of a bead, similar to the attached pic or less? (pic taken from another thread

http://forums.bimmerforums.com/forum...nal-RTV-or-not

- I was thinking that as long as there is sealant that squeezes out after tightening then I've applied enough) I'm thinking the RTV is probably paper thin when the bolts are fully tightened and torqued.

- Speaking of torque, bentley says 7ft lbs (= 10nms), I was thinking this was info given out there so not to risk cracking OE composite housing, would an aluminum housing require (and withstand) more torque?

- Also, after applying the RTV on the housing did you immediately attach and tighten to torque specs or did you wait some time?

Maybe I'm paranoid, but I've been checking it almost daily as I like to have the car hood open to vent the heat out. No leaks whatsoever. I've used gray permatex designed for thermostat housing (highest coolant leak resistance). I've basically smeared very thin smear (not the bead) around the outside perimeter of housing, but making sure to not interfere with either gasket or o ring.

Even though I agree with the argument that sealant is not required on E39 TH design, the reality is different, at least in my case. My thinking is that combination of slightly imperfect surfaces on either housing or head side and some other factors simply require added leak protection in form of sealant.

I've still only used 10nm and little bit of blue Loctite on bolts, since torque is so low that theoretically bolts may come loose without it.

I've waited maybe 5 min before torqueing it since smear is so thin that I was afraid that it would get to dry.

[achtung98m]

Maybe I'm paranoid, but I've been checking it almost daily as I like to have the car hood open to vent the heat out. No leaks whatsoever. I've used gray permatex designed for thermostat housing (highest coolant leak resistance). I've basically smeared very thin smear (not the bead) around the outside perimeter of housing, but making sure to not interfere with either gasket or o ring.

Even though I agree with the argument that sealant is not required on E39 TH design, the reality is different, at least in my case. My thinking is that combination of slightly imperfect surfaces on either housing or head side and some other factors simply require added leak protection in form of sealant.

I've still only used 10nm and little bit of blue Loctite on bolts, since torque is so low that theoretically bolts may come loose without it.

I've waited maybe 5 min before torqueing it since smear is so thin that I was afraid that it would get to dry.

Response greatly appreciated!

"smear" i think thats the right amount, should expect hardly any RTV to squeeze out once the bolts are tightened

[AusE39er]

Very happy that my early M52 engine has the aluminum one, I am not worried at all about it developing a leak.

[cnn]

I discussed this with the O.P. (siny528i), and his repair using RTV still holds up fine.

I have a different issue, the BMW OEM Plastic tstat housing becomes warped every 2 years/20K. Initially I thought it was the gaskets causing the leak, but after I removed the plastic housing and place it on a flat surface, it became clear that the cause of the leak is from plastic warping.

The issue with after market aluminum tstat housing is that: it is somewhat not perfectly flat. But this is an easy fix.

- Get piece of granite tile ($8 at hardware store) or a piece of porcelaine floor tile ($6 at hardware store), place a 600-grit sandpaper on it. Glass tabletop works too but make sure you don't damage the expensive table!

- Slide the Aluminum tstat housing back and forth on the sandpaper for a good 15 minutes until it is really shiny and smooth.

- Place the aluminum tstat housing on the flat surface to check for flatness. Any gap less than a piece of paper is fine b/c the paper gasket paper +RTV will fix it.

- NOTE that I used E34-E36 M50 Paper Gasket (PN in the photos). Trim it a bit as shown to clear the Orange gasket. I used the Orange gasket that came with the URO aluminum tstat housing. I bought two (2) M50 Paper Gasket b/c it is cheap ($1/each) and just in case I messed it up. But it went fine, so I have a spare gasket in the garage...

- Install the Oranage Gasket. Now apply a thing smear of Black RTV on both sides of the paper gasket. Lay it on the aluminum tstat housing. Let is sit for a good 15 min, so it is a bit tacky.

- Install the aluminum tstat housing + Orange Gasket + Paper Gasket (with a thin smear of RTV) dry. Do NOT fill with coolant yet. I let the RTV cure for about 3-4h. Then add coolant and test drove it.

- So far for the first 200 miles, bone dry no leak!!!

- Normally, I am not a fan of URO products, but this URO Aluminum Tstat Housing is fine.

- I highly recommend Aluminum Housing + sandpaper + M50 paper gasket + RTV trick.
We will see how long this URO Aluminum thingy lasts...


PS: For those of you who are new to this (info in forum):

a. The Fan Clutch is REVERSE thread, apply a bit of antiseize during install.

b. Observe the torque values, do NOT strip the bolts.

c. Filling with coolant: open the bleeder bolt (do NOT lose it!). SLOWLY fill with coolant, you need to be patient. You may have to go a bit above "KALT" on the reservoir to allow coolant to overflow a bit out of the bleed port. Reinstall the bleeder bolt finger tight.

d. Clean the area with some degreaser and water, this way any new leak is easily seen.

See the photos!

E39-Tstat-02.jpg E39-Tstat-03.jpg E39-Tstat-04.jpg E39-Tstat-01.jpg

E39-Tstat-05.jpg

[jclausen]

I would use only BMW gaskets not the ones that could come with the housing, some times the head surface area where the thermostat gaskets seal will get electrolysis, fill and sand smooth with jb weld

[geargrinder]

I like the sand-on-glass suggestion. Sounds like a good attempt to resolve a tricky situation with 2 parts available, but each flawed in a different way.

[cnn]

I would use only BMW gaskets not the ones that could come with the housing, some times the head surface area where the thermostat gaskets seal will get electrolysis, fill and sand smooth with jb weld

Although I agree with you that aftermarket seal is not as good as BMW seal, the aftermarket Orange seal is somewhat taller than the BMW seal by almost 1.5 mm. Maybe this is from the BMW seal being squeezed for 2 years, I do not know.

Since:
1. I do not want to deal with this again, I err on the taller seal, and
2. There is a paper gasket on the peripheral edge as "double safety",

I feel safe using aftermarket URO seal.

Anyway, the area is so pristine clean, bone-dry after some 500 miles. It looks as nice as my previous E23 1983 735i with Aluminum tstat housing back in the good old days.

I am now an Aluminum convert, I no longer advocate OEM Plastic housing having gone through 3 of them in the last 10 years. Hopefully this Aluminum thingy is the last Tstat housing I ever need...