Thermostat Housing Leaks After Replacing Thermostat

[donb318]

I replaced my thermostat over the weekend and it wasn't too bad. But afterward, coolant came leaking out of the housing near the lower left-hand mounting bolt. I installed an original looking housing gasket but was there more I needed to do? Do I need a new housing or just use some silicone sealant? 1992 318i Build 7/92.

[Nanniepoo]

I'm not familiar with the 4-bangers, but assuming they're similar to the M50/M52, BMW considered the plastic housings a one-time use. That's debatable but you definitely need a new gasket and likely some RTV.

[thenjnick]

If you have the aluminum housing, that can be reused with a thin layer of rtv on the gasket. I went with the elring gasket (no rtv), no leaks yet. Good luck


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[E36328Coupe]

Nothing up with the 6 pot thermostat housings, mostly, if not near always, down to bad technique fitting when they crack

[donb318]

I'm not familiar with the 4-bangers, but assuming they're similar to the M50/M52, BMW considered the plastic housings a one-time use. That's debatable but you definitely need a new gasket and likely some RTV.

Yeah its an M42. I have the aluminum housing.

[donb318]

If you have the aluminum housing, that can be reused with a thin layer of rtv on the gasket. I went with the elring gasket (no rtv), no leaks yet. Good luck


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I did not even see a gasket when I removed the housing. Maybe it completely deteriorated. The new housing gasket has two thin beads but probably wasn't enough. I think the mechanic I had replace the thermostat years ago used RTV.

[thenjnick]

I did not even see a gasket when I removed the housing. Maybe it completely deteriorated. The new housing gasket has two thin beads but probably wasn't enough. I think the mechanic I had replace the thermostat years ago used RTV.

Mine was the same way. Only a millimeter of gasket left if even that and it took a lot of wire brushing to get the remnants off. My gasket had the pre-beaded rtv as well so i decided not to use more. Maybe the housing is warped enough to drip? I checked mine with a metal ruler and it looked alright. I also cleaned the mating surface really, really good and positioned it on super carefully. I’m convinced my OCD helped me on this one.


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[myblackcar]

Use RTV on the aluminum gasket surface. Don't bother with a gasket. The aluminum housings never had a good mating surface. Also check if there is no debris on the mating surface.

[donb318]

Mine was the same way. Only a millimeter of gasket left if even that and it took a lot of wire brushing to get the remnants off. My gasket had the pre-beaded rtv as well so i decided not to use more. Maybe the housing is warped enough to drip? I checked mine with a metal ruler and it looked alright. I also cleaned the mating surface really, really good and positioned it on super carefully. I’m convinced my OCD helped me on this one.


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Come to think of it, my housing might be warped because I noticed the bolts weren't torqueing evenly. I'd get them torqued but then tightening one would make the rest need further tightening. I kept having to go around and around until they seemed to all decide to finish torqueing.

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Use RTV on the aluminum gasket surface. Don't bother with a gasket. The aluminum housings never had a good mating surface. Also check if there is no debris on the mating surface.

That was going to be my next question if using RTV still requires the gasket. I guess it depends on if you use a thick bead or a thin one.

[thenjnick]

Come to think of it, my housing might be warped because I noticed the bolts weren't torqueing evenly. I'd get them torqued but then tightening one would make the rest need further tightening. I kept having to go around and around until they seemed to all decide to finish torqueing.

Thats sounds pretty normal to me. Did you use a torque wrench? I tightened them by hand but not too much, not as much as i wanted to at least haha but the housing is pretty soft so it could have bent easily..maybe just enough rtv will do the trick? I think they run ~$90 on fcp iirc

[donb318]

Thats sounds pretty normal to me. Did you use a torque wrench? I tightened them by hand but not too much, not as much as i wanted to at least haha but the housing is pretty soft so it could have bent easily..maybe just enough rtv will do the trick? I think they run ~$90 on fcp iirc

I torqued to the specified 89 inch/lbs. $90 for RTV? Wha what?

[thenjnick]

I torqued to the specified 89 inch/lbs. $90 for RTV? Wha what?

No I meant the thermostat housing sorry. Its $53 on pelican plus shipping.

https://www.pelicanparts.com/More_In...SVSVSI=128.htm

I think you should be fine if you replace it and just put a new gasket with rtv to be safe, otherwise just use a generous amount of rtv on the old housing.

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[donb318]

Generous amount of RTV would be a quicker fix but a new housing would be ideal. I found an OEM housing on eBay with gasket for $55, free shipping, no tax.

[thenjnick]

Good deal. Let us know how it goes. I have to go top off my rad and bleed again, thing is overheating now. Hopefully im not losing coolant and some air is trapped in there. Ugh


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[donb318]

Will let you know when I get it done. I have two BMW's and so I'm not really in a hurry. Probably next weekend. When I had air in my coolant system, it would over heat right away. I actually didn't bleed it at all. But once I bled it, all was well. I have a new radiator, water pump, fan clutch, radiator cap and fan shroud though. Thermostat just recently started sticking.

[thenjnick]

Not sure why mine is starting to overheat all of a sudden, everything was fine since i put in a new radiator two weeks ago. My brother uses the car 5 days a week so I dont get much time to look it over. Hoping a refill and bleed will do the trick. We’ll see


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[BMWManiac]

Not sure why mine is starting to overheat all of a sudden, everything was fine since i put in a new radiator two weeks ago. My brother uses the car 5 days a week so I dont get much time to look it over. Hoping a refill and bleed will do the trick. We’ll see


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Probably just needs to be bled some more

[donb318]

Not sure why mine is starting to overheat all of a sudden, everything was fine since i put in a new radiator two weeks ago. My brother uses the car 5 days a week so I dont get much time to look it over. Hoping a refill and bleed will do the trick. We’ll see


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What's it actually doing?

I believe when there is air in the system, the temp gauge will intermittently shoot into the red. At least that's what mine did.

[woody328is]

Maybe it's possible that the thermostat moved out of position before bolting the housing down tight. If so that may explain the odd bolt tightening and leak. Seems like you need to remove it and recheck.

[donb318]

Maybe it's possible that the thermostat moved out of position before bolting the housing down tight. If so that may explain the odd bolt tightening and leak. Seems like you need to remove it and recheck.

I opened it back up and the thermostat was still in place, spot on. I'm just gonna replace the housing.

[woody328is]

Smart move. It was just a thought.

[thenjnick]

Probably just needs to be bled some more

Agreed. I topped it off and bled it yesterday, ran it for a while with no overheating. Ill check the level tomorrow.

What's it actually doing?

I believe when there is air in the system, the temp gauge will intermittently shoot into the red. At least that's what mine did.

I honestly don’t know what happened prior to it shooting into the red, I tried to get more info but no go. I think trapped air is a good bet, however the aux fan isn’t being triggered by the temp switch or the AC plus it was a hot day so that’s most likely the cause. Could there be such a large air pocket that left me over a liter dry on coolant even after driving it a few days without issue? I did drain the block too..still seems odd to me

Im just worried about the condition of the head gasket at this point. The car has overheated a few times now and im hoping to do a compression/leak down test soon.


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[thenjnick]

Sorry I dont mean to threadjack...


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[Tar Baby]

Shoulda used plastic maybe.....

[Migou]

When I changed my t/stat housing I sanded it flat before installing. Even brand new it was a bit warped. Granted it was on a 6 cyl.