Thermostat housing O-ring

[SoloTSi97]

Sorry to revive an old thread but any idea if there's a solution to this? The seal in my housing is shot and no longer seals against the thermostat. Turns out, that's probably been the cause of my "implausible temperature" codes for a while now. But, the housing itself is NLA ... dealer confirmed that there are zero in the US & zero in Germany. Of course, I can source a used one but that's going to be a bit of a gamble (that's only going to get worse as these cars continue to age).

Any chance some enterprising soul in the aftermarket has come up with a viable solution here?

[ac427]

Sorry to revive an old thread but any idea if there's a solution to this? The seal in my housing is shot and no longer seals against the thermostat. Turns out, that's probably been the cause of my "implausible temperature" codes for a while now. But, the housing itself is NLA ... dealer confirmed that there are zero in the US & zero in Germany. Of course, I can source a used one but that's going to be a bit of a gamble (that's only going to get worse as these cars continue to age).

Any chance some enterprising soul in the aftermarket has come up with a viable solution here?

How many miles has your car done?

Mine has done 180k miles on the original thermostat housing. Perhaps yours got damaged or had a manufacturing defect.

[SoloTSi97]

How many miles has your car done?

Mine has done 180k miles on the original thermostat housing. Perhaps yours got damaged or had a manufacturing defect.

149k on the clock here. I don't think it's a common failure point (yet) but it stands to reason a seal could over time degrade I guess. I'm not sure the history of mine but it pretty clearly doesn't seal fully against the thermostat housing.

[ac427]

149k on the clock here. I don't think it's a common failure point (yet) but it stands to reason a seal could over time degrade I guess. I'm not sure the history of mine but it pretty clearly doesn't seal fully against the thermostat housing.

I had one on order for months and cancelled it in the end.

It's probably worth getting a secondhand one just to confirm it fixes the fault, with a view to getting a new one at a later date.

[SoloTSi97]

I had one on order for months and cancelled it in the end.

It's probably worth getting a secondhand one just to confirm it fixes the fault, with a view to getting a new one at a later date.

Yeah, my local parts guy said he saw zero in the US and zero in Germany. I'm not sure if there will be more at a later date or not.

So yeah, I think the hunt for a good used one begins!

[ac427]

Yeah, my local parts guy said he saw zero in the US and zero in Germany. I'm not sure if there will be more at a later date or not.

So yeah, I think the hunt for a good used one begins!

"Back order with no ETA" i was told by the parts department. So unless we order 10 each there will be none made.

[RobE36E46]

I think I might need one of these as well. Restoring an M3 that was kept in a hanger in northern Montana for a decade and driven sparingly. 80k miles now.

Just replaced original T-stat, O-rings (coolant pipes too), and saw evidence of a coolant leak near the housing….well it’s back. I cleaned everything thoroughly and torqued to 10 N-m. WTF? 🤬 and the part is not available - double WTF.

What did people end up doing?

[Ramo]

I think I might need one of these as well. Restoring an M3 that was kept in a hanger in northern Montana for a decade and driven sparingly. 80k miles now.

Just replaced original T-stat, O-rings (coolant pipes too), and saw evidence of a coolant leak near the housing….well it’s back. I cleaned everything thoroughly and torqued to 10 N-m. WTF? 🤬 and the part is not available - double WTF.

What did people end up doing?

when you were putting back the thermostat housing did you pop it back into the coolant pipe first try or after multiple tries?

because the first time I did mine it wouldn't go in and I kept adjusting it, pushing in and out and I finally popped it in when I put some grease. When I started the car I had a leak. Took of the thermostat housing and turns out I had ripped a part of the coolant pipe o ring at the bottom when I was trying to pop it on before I put grease but I couldn't see the it ripped since it was the bottom part of the o ring. I replaced the o ring with a new, applied a small amount of grease and carefully put the housing into the pipe first try and no leaks.

[RobE36E46]

Ramo - Thank you for the input! Definitely multiple tries and I have been suspicious that this could be the source of my leak.

I did both ends of the pipe and order the "OE supplier ones" from FCP. They seemed to be too large (loose on the pipe) and I broke the second one getting it on (Similar to your pic). It seems that you get a small portion that doesn't engage into the housing (a small loop) and then when I forced this, it ripped the O-ring. I replaced it (I had ordered 4 just in case since they were like $1 ea).

I lubricated with coolant and used either my fingers or a screw driver to gently press "the loop" it in place and confirmed (or thought I did) proper engagement all around with an inspection mirror.

With a mirror, I can see a coolant drip coming right down between the waterpump and thermostat housing (pic below). Where was your leak coming from? I'm thinking maybe I can wrap the coolant pipe - to thermostat with a paper towel and see if it gets wet to see if that is where the leak is?

The other oddity is a couple of times my temperature gauge has fallen from 12:00 to say 11:30 when going downhill and off the throttle. None of my M5xs have ever done this, so that seemed suspicious to me as well. It was also doing this on the original T-stat and I boiled both (in our pasta pot, my wife loved that....) and it seemed like the old one was opening early. The not staying at 12 o'clock is better now for sure, but I am suspicious that the coolant gauge is still moving.

Anyway I really appreciate all the advice and thoughts!

[Slideways]

Ramo - Thank you for the input! Definitely multiple tries and I have been suspicious that this could be the source of my leak.

I did both ends of the pipe and order the "OE supplier ones" from FCP. They seemed to be too large (loose on the pipe) and I broke the second one getting it on (Similar to your pic). It seems that you get a small portion that doesn't engage into the housing (a small loop) and then when I forced this, it ripped the O-ring. I replaced it (I had ordered 4 just in case since they were like $1 ea).

I lubricated with coolant and used either my fingers or a screw driver to gently press "the loop" it in place and confirmed (or thought I did) proper engagement all around with an inspection mirror.

With a mirror, I can see a coolant drip coming right down between the waterpump and thermostat housing (pic below). Where was your leak coming from? I'm thinking maybe I can wrap the coolant pipe - to thermostat with a paper towel and see if it gets wet to see if that is where the leak is?

The other oddity is a couple of times my temperature gauge has fallen from 12:00 to say 11:30 when going downhill and off the throttle. None of my M5xs have ever done this, so that seemed suspicious to me as well. It was also doing this on the original T-stat and I boiled both (in our pasta pot, my wife loved that....) and it seemed like the old one was opening early. The not staying at 12 o'clock is better now for sure, but I am suspicious that the coolant gauge is still moving.

Anyway I really appreciate all the advice and thoughts!

Those "OES" o-rings from FCP are slightly too large. While they can work if you lubricate them with silicone and pay very close attention during install to not pinch them, it is better to stick to the OE BMW o-ring for this part.

[dl.m3]

Wow i thought i was going crazy because i had the exact same problem with the FCP OE pair of O-rings for this coolant pipe. It was just a tad too big. I managed to muscle one of them in with grease and patience but had to re-use the old one for the other. What a pain.

[Ramo]

Ramo - Thank you for the input! Definitely multiple tries and I have been suspicious that this could be the source of my leak.

I did both ends of the pipe and order the "OE supplier ones" from FCP. They seemed to be too large (loose on the pipe) and I broke the second one getting it on (Similar to your pic). It seems that you get a small portion that doesn't engage into the housing (a small loop) and then when I forced this, it ripped the O-ring. I replaced it (I had ordered 4 just in case since they were like $1 ea).

I lubricated with coolant and used either my fingers or a screw driver to gently press "the loop" it in place and confirmed (or thought I did) proper engagement all around with an inspection mirror.

With a mirror, I can see a coolant drip coming right down between the waterpump and thermostat housing (pic below). Where was your leak coming from? I'm thinking maybe I can wrap the coolant pipe - to thermostat with a paper towel and see if it gets wet to see if that is where the leak is?

The other oddity is a couple of times my temperature gauge has fallen from 12:00 to say 11:30 when going downhill and off the throttle. None of my M5xs have ever done this, so that seemed suspicious to me as well. It was also doing this on the original T-stat and I boiled both (in our pasta pot, my wife loved that....) and it seemed like the old one was opening early. The not staying at 12 o'clock is better now for sure, but I am suspicious that the coolant gauge is still moving.

Anyway I really appreciate all the advice and thoughts!

The leak was coming from the Bottom of the oring in front of the coolant pipe. The 2nd time I redid it I used the high temp o ring WOLFN8TR sells.

[SoloTSi97]

Well, four supposedly brand new OEM thermostat housings showed up on ebay last week from Lithuania. I'm super skeptical but it was enough to prompt me to pull mine back apart to convince myself whether or not it was worth taking the risk by ordering one.

I tested my old thermostat alongside a(nother) brand new one in hot water and both opened at about the same temp and opened the same amount as measured with a caliper. So, both old and new thermostats appear to be good.

One thing I noticed is that there are marks on the old thermostat where the housing seal has rubbed against the thermostat body as it opened and closed. But, there's about a 3cm section where there are no marks on the thermostat. I wonder if the housing seal is not sealing against the thermostat in that spot and is allowing coolant past the thermostat, leading to my problem. It at least seems like a plausible theory.

So, I ordered one of the available housings on ebay. Hopefully it's not a scam (or if it is, hopefully ebay/paypal are easy to work with). I'll report back.

[m3_sancho]

Since we're talking about thermostats. I took mine apart and found a rubber band around the thermostat sitting in the housing. I don't see that in the diagram. Anybody knows what that is and if that belongs there?