Thermostat housing O-ring

[Acer619]

You can try getting O-Ring from a pump manufacturer like Davey Malaysia.

They have various pump sizes because of their pump assortment and product variations, but they should have it.

These O-rings are used to secure placements between fittings, so I'm sure you'd get what you need...

[SoloTSi97]

I'm trying to understand the problem, is your car overheating? Is it not getting up to temp? You have a fault code, but the car drives wonderfully?

tl;dr: It's now driving fine but I'm getting a fault code due to engine temp plausibility.

For a long time, the temp gauge never came up past the bottom dot (1/4 mark) and I frequently had a SES light due to engine temp plausibility. I had already replaced the tstat and both temp sensors (lower rad hose and behind the tstat housing) as an attempted fix but still had the same symptom. After reading about this tstat housing seal that can apparently stop sealing, I figured that was the cause and got busy with other things. A few years went by. Lol

Since some supposedly new tstat housings popped up recently on eBay, I ordered one along with a new tstat, water pump, sensors, hoses, etc, and figured I'd just do a cooling system refresh since I'd never done it. The tstat housing ended up falling through but I replaced everything else.

Now, the temp gauge is working! It comes up to the middle and moves around between 1/4 & 3/4 like it should. But, I'm still getting the SES light for the temp plausibility code. So, it's better... but not fixed.

[332]

I'm trying to understand the problem, is your car overheating? Is it not getting up to temp? You have a fault code, but the car drives wonderfully?

[SoloTSi97]

Well, it seems that my thermostat housing wasn't the problem after all! I decided to double check everything I could think of while I had it apart again. Turns out, the coolant temp sensor under the intake manifold (next to the oil filter housing) wasn't reading properly. At room temperature (~70F), it was reading 4500 ohms. From what I'd read online, it should have been around 2100. I grabbed a new sensor from my local parts store and indeed it read 2100 ohms at the same temperature.

It's all back together now and the temperature gauge came right up to dead center for the first time in years! I had replaced this sensor before so had checked it off the list of possible causes. I guess I got a defective one. I'll probably get it replaced at FCP (where I bought it) so I have a spare.

I'm still on the lookout for a spare tstat housing, though, just in case!

Aaaand I spoke too soon. 🙃

The temperature gauge is working now, which is a nice change. But, after a few days the temperature plausibility code came back. So, I think I'm back where I started ... hunting for a thermostat housing.

[SoloTSi97]

Well, it seems that my thermostat housing wasn't the problem after all! I decided to double check everything I could think of while I had it apart again. Turns out, the coolant temp sensor under the intake manifold (next to the oil filter housing) wasn't reading properly. At room temperature (~70F), it was reading 4500 ohms. From what I'd read online, it should have been around 2100. I grabbed a new sensor from my local parts store and indeed it read 2100 ohms at the same temperature.

It's all back together now and the temperature gauge came right up to dead center for the first time in years! I had replaced this sensor before so had checked it off the list of possible causes. I guess I got a defective one. I'll probably get it replaced at FCP (where I bought it) so I have a spare.

I'm still on the lookout for a spare tstat housing, though, just in case!

[SoloTSi97]

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?

Mine did not have that and I agree that I don't see it on any parts diagram.maybe that's someone's attempt to solve this problem? Hmm.

Did you have issues with your car never getting up to temp or was your thermostat operating correctly? If the thermostat works the way I think it works, any way to seal the gap between the thermostat itself and the housing surface would accomplish the same goal as the original seal. Hmm again.

Side note, I got a message from the eBay seller in Lithuania that they "seem unable to find this part." I knew it was too good to be true. All four listings from different sellers who I'm sure are really the same seller are now marked out of stock.my guess is they planned to source the item from BMW and discovered that they cant. Ah well.

Hello, I want to write you as soon as possible, about this urgent matter.
We requested our warehouse to recheck the location before shipping it out, but unfortunately, they seem unable to find this part, and we had only one in our inventory.
It’s possible that this item was sold and the system wasn’t updated in time.
We sincerely apologize for the inconvenience.
We suggest you to do not keep this order on hold for too long, because it is possible to lose a BUYERS PROTECTION after this time. So we recommend you CANCEL this order using the CANCEL ORDER button in your order details. We will notify you when the item is back in stock.
Sincerely

[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?

[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.

[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.

[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.

[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.

[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!

[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]

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?

[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.