How to safely clean thermostat housing mating surface

[hexdump]

Hey all,

I'm currently replacing my leaky thermostat housing (along with much of the rest of the cooling system, previously replaced in 2014). I'm replacing it with a brand new genuine BMW plastic housing with a built-in gasket.

I'm wondering how to clean this thermostat housing mating surface as well as the water pump mating surface (the slightly discolored area at the bottom of the hole).

These pics are AFTER scrubbing with a nylon brush, a plastic scraper and a microfiber towel soaked with brake cleaner. For about an hour. It's pretty smooth, I can barely feel the dirt when I run a finger over it. Is that good enough or does it really need to be pristine looking?

tstat_housting_mating_surface.jpg

water_pump_surface.jpg

I'm reluctant to use a brass brush or sandpaper for fear of scratching the soft aluminum.

Thanks

[Eric93se]

The water pump looks good. I would use very fine sandpaper for the thermostat housing perimeter, maybe 800 grit wet with wd40, gentle circular motion to get the residue off. You have some pitting there but it should be fine. If you want you can put a very thin smear of Permatex RTV silicone on the thermostat housing, very thin meaning a paper thin smear. I've had my car for 13+yrs and when I did the cooling system I actually re-used the plastic housing and didn't use any sealant and its been overall fine, but if the car sits the housing can seep a couple drops, when I do it again I will put the RTV with a new housing.

You can clean the threads on the WP threads with a wire brush. Some people would put new studs but I would be afraid of snapping one off when extracting. Make sure you use a good torque wrench when installing all these nuts/bolts because the torque required is very low.

Some people might fill the pitting with JB weld epoxy, you would use a razor blade to fill the pit and drag it across to get it perfectly flat.

[hexdump]

The water pump looks good. I would use very fine sandpaper for the thermostat housing perimeter, maybe 800 grit wet with wd40, gentle circular motion to get the residue off. You have some pitting there but it should be fine. If you want you can put a very thin smear of Permatex RTV silicone on the thermostat housing, very thin meaning a paper thin smear. I've had my car for 13+yrs and when I did the cooling system I actually re-used the plastic housing and didn't use any sealant and its been overall fine, but if the car sits the housing can seep a couple drops, when I do it again I will put the RTV with a new housing.

You can clean the threads on the WP threads with a wire brush. Some people would put new studs but I would be afraid of snapping one off when extracting. Make sure you use a good torque wrench when installing all these nuts/bolts because the torque required is very low.

Some people might fill the pitting with JB weld epoxy, you would use a razor blade to fill the pit and drag it across to get it perfectly flat.

Thanks for the info, I will try out the sandpaper tomorrow.

I took a look at the thermostat housing that I got and I'm a bit confused. Isn't the Genuine BMW version supposed to have a gasket across the entire mating surface in addition to the orange profile gasket?

Mine doesn't seem to have anything. It is listed as a genuine BMW version from FCP euro.

housing.jpg

I was expecting something like this: (credit: https://www.dvatp.com/bmw/thermostat)
e36_tstat_housing_with_profile_gasket_large.jpg

[bluptgm3]

Do not use the oversized gasket even IF it is OE.

Use the aftermarket Elring gasket.


From what I have read, URO is using what they claim is similar to or is the current BMW OE orange ‘thingie’ gasket.
Used original gasket, older unused URO, newer URO and on the right Elring (similar to original OE) shown below.




There is a very good thread on this forum with regard to the issue of T-Stat housing failures due to oversized gaskets

[hexdump]

Do not use the oversized gasket even IF it is OE. Use the aftermarket Elring gasket.



There is a very good thread on this forum with regard to the issue of T-Stat housing failures due to oversized gaskets

Hey thanks but I'm not talking about that orange gasket. I was referring to the gasket that goes all the way around the mating surface on the housing itself.

See these pics: bottom right pic on this page https://www.dvatp.com/bmw/thermostat or https://www.fcpeuro.com/public/asset...w4.?1496476830

RealOEM says that my there is no paper gasket for my VIN so I feel like the housing should have a bonded gasket that comes with it, no?

[bluptgm3]

Hey thanks but I'm not talking about that orange gasket. I was referring to the gasket that goes all the way around the mating surface on the housing itself.

RealOEM says that my there is no paper gasket for my VIN so I feel like the housing should have a bonded gasket that comes with it, no?

Yah, the circular opening is sealed by the thermostat oring gasket.
No real need for that surface to be perfect.



Again, do not use the new and improved oversized OE or URO ‘orange thingie’ gasket.
Resist the temptation to use sealant.

[hexdump]

Not the circular opening. The part all around the housing surface. The green portion of this picture: https://www.fcpeuro.com/public/asset...w4.?1496476830

[bluptgm3]

Not the circular opening. The part all around the housing surface. The green portion of this picture: https://www.fcpeuro.com/public/asset...w4.?1496476830

Not seen this before. OE T-stat housings of years past did appear to have an ever so slight film but nothing that would bond that surface.

I believe the NV engines T-Stat housing didn’t have the gasket grove and used a gasket that does not fit properly on these grooved housings. However that housing and gasket is no longer offered, replaced by the later configuration.

[hexdump]

So if my housing did not come with the green gasket, do I need to use RTV all around or something else? I'm tempted to exchange it for one that does have the green gasket.

I'm not sure what you mean by the oversized gasket. Is the one I have (pic in post #3) oversized? It's a genuine BMW housing and the orange gasket came with it. There was no oversized option.

[Eric93se]

He's referring to the orange gasket, not to use a thick one.

As I stated the composite (black) housing does not use a profile gasket, mine is installed without one and without rtv. Mine does seep a tiny amount, and I suggested you use a thin film of rtv basically where you see that green gasket. That green gasket came about a few years ago, as you can see its not on the official OEM parts diagram.

10+ years ago the metal housing came around and they leaked, manufacturers did not make the face flat, so people had to sand them flat

[bluptgm3]

He's referring to the orange gasket, not to use a thick one.

As I suggested, read this thread for gasket discussion

10+ years ago the metal housing came around and they leaked, manufacturers did not make the face flat, so people had to sand them flat

As for the 20+ year aluminum die cast T-Stat housings, I believe it was porosity issues that caused leaking. I had one that weeped thru the face of the casting. When I replaced it, the flaw in the casting was obvious

[Eric93se]

People were taking a piece of glass and taping a sheet of sandpaper to it and wet sanding the face flat.

[hexdump]

He's referring to the orange gasket, not to use a thick one.

Thanks Eric, understood but what is considered "thick" here? I would imagine that the one that came with the BMW housing would be standard and not too thick. I'm fine to order the Elring gasket as a replacement but it looks pretty much exactly the same as the gasket that is on my housing.

As I stated the composite (black) housing does not use a profile gasket, mine is installed without one and without rtv. Mine does seep a tiny amount, and I suggested you use a thin film of rtv basically where you see that green gasket. That green gasket came about a few years ago, as you can see its not on the official OEM parts diagram.

10+ years ago the metal housing came around and they leaked, manufacturers did not make the face flat, so people had to sand them flat

Gotcha, when I read your first post I assumed my housing (which I ordered a few months ago) would have the green gasket and that yours had it as well so I didn't really understand why you used RTV in addition. Now it makes sense though: you don't have the green gasket either.

I agree, it doesn't seem like a good idea to run this housing without any RTV and no green gasket. So my options are either 1) exchange the housing for one that has a green gasket or 2) run this one with RTV. I'm more inclined to the former option since one edge of the housing is very thin and it seems like it would be harder to get a decent, yet thin, coat of RTV onto it. Also, it appears that my previous housing (installed in 2014) also didn't have the green gasket but I did put a thin coat of RTV and it leaked (eventually). So I would hope the green gasket would be an improvement. I'll call FCP Euro tomorrow and see if they'd be willing to exchange it.

[hexdump]

As I suggested, read this thread for gasket discussion



As for the 20+ year aluminum die cast T-Stat housings, I believe it was porosity issues that caused leaking. I had one that weeped thru the face of the casting. When I replaced it, the flaw in the casting was obvious

Good discussion! I now understand that the gasket that comes with the OE housing also isn't good (too thick). Shocking how this simple aspect of a car design can be so hard to get right for the OEMs and aftermarket manufacturers.

I will order the Elring gasket and probably a Febi housing since that one appears to have the green gasket as well.

[bluptgm3]

I will order the Elring gasket and probably a Febi housing since that one appears to have the green gasket as well.

Don’t think the ‘green’ is a gasket, I suspect the color comes from a pre-applied (and cured) sealant. May not bond to the head, however will act as a separate gasket.

[Eric93se]

Rockauto has it.

https://www.rockauto.com/en/catalog/...tlet+seal,2136

- - - Updated - - -

I would use the felpro.

[hexdump]

Don’t think the ‘green’ is a gasket, I suspect the color comes from a pre-applied (and cured) sealant. May not bond to the head, however will act as a separate gasket.

Yep, functionally a gasket but really a sealant.

Rockauto has it.

https://www.rockauto.com/en/catalog/...tlet+seal,2136

- - - Updated - - -

I would use the felpro.

You mean this guy? https://www.rockauto.com/en/moreinfo...pt=2136&jsn=21

I think that is a paper gasket meant for the '92 cars. I could be wrong. You're saying you would use that in addition to my existing housing?

- - - Updated - - -

Here is the cleaned mating surface. I used 1000 grit sanding paper, followed up with some 0000 steel wool. Shop vac, brake cleaner on a rag, shop vac again. Good enough?

tstat_housting_mating_surface_cleaned.jpg

[bluptgm3]

You mean this guy? https://www.rockauto.com/en/moreinfo...pt=2136&jsn=21

I think that is a paper gasket meant for the '92 cars. I could be wrong. You're saying you would use that in addition to my existing housing?

Yah, hate to admit this but I bought this gasket from the dealer years ago. It does not fit due to the trough for the orange gasket.

[Eric93se]

The link I gave is for a '97 328i, if you click that link, find the felpro part and then click on the part number it will list all the cars its supposed to fit (includes yours). If that gasket doesn't fit with the orange seal I believe people trimmed it to fit.

Next time I do this job I will use rtv and a metal housing (and the orange gasket lol)

Blupgtm3, is that pic from your car? That's some heavy pitting.

Just to note, the OEM diagram above depicts the option to use the orange gasket OR the paper profile gasket.

[hexdump]

The link I gave is for a '97 328i, if you click that link, find the felpro part and then click on the part number it will list all the cars its supposed to fit (includes yours). If that gasket doesn't fit with the orange seal I believe people trimmed it to fit.

Next time I do this job I will use rtv and a metal housing (and the orange gasket lol)

Blupgtm3, is that pic from your car? That's some heavy pitting.

Just to note, the OEM diagram above depicts the option to use the orange gasket OR the paper profile gasket.

So you won't use the paper gasket yourself because you are going to use a metal housing? But you suggest I do since I have a plastic housing with no "green gasket"? Am I understanding correctly?

I am not so convinced of the advantages of the metal housing myself. People say the plastic cracks but it hasn't cracked at all for me since I bought this car in 2006. Granted, it's a DD and not a race car but still. Plus, there isn't really a OEM-quality metal housing part. It seems they are all cheap-o brands. Why doesn't Febi or Mahle or a more reputable company like that make one? The discussion blueptgm3 linked to (https://www.bimmerforums.com/forum/s...ecommendation/) also confirms that the tide of opinion may be shifting back to OEM plastic housings. That said, I'm not opposed to getting a metal housing either if I can be convinced of a good reason to do it.

One other issue I noticed. The "genuine BMW" housing I received does not have any BMW roundel logo stamped onto it. The old one that I removed from the car did have one. Aren't genuine BMW parts supposed to have the logo stamped onto them? I will have to call FCP euro today to discuss this.

[bluptgm3]

Here is the paper gasket on the later model T-Stat housing. Early T-Stat housings did not have the trough or groove for the orange gasket.

[hexdump]

Here is the paper gasket on the later model T-Stat housing. Early T-Stat housings did not have the trough or groove for the orange gasket.

Right, that clearly won't work and I suspect the fel-pro gasket sold by rockauto would be the same way. I don't think the post-92 housings support a paper gasket.

[Eric93se]

Well if your good with an xacto knife you can trim the gasket to accept the orange gasket, I think that would be best (people have done this). Any you do what you think is best, by now your an expert

With any changes to the cooling system you should monitor it anyway.

[bluptgm3]

Well if your good with an xacto knife you can trim the gasket to accept the orange gasket, I think that would be best (people have done this). Any you do what you think is best, by now your an expert

With any changes to the cooling system you should monitor it anyway.

There is the added height of the gasket to consider. The orange ‘thingie’ gasket and T-Stat O-ring are attempting to seal the housing-to-head gap. Any change impacts the ability of those two seals to contact their respective seal planes.

[Eric93se]

I think it will be alright.

Hexdump, what temp thermostat are you planning on running? Personally I use an 80c stat, less pressure on the systems plastic parts. You can find cooler thermostats by selecting an '88 325i, personally I don't think going below 80c is a good idea though but I've been using the 80c for over 10yrs now with no I'll effects.