Next person to replace coolant temperature sensor: Please measure the O-ring size!

bluebee · Aug 1, 2010

Can someone tell us the specification for the coolant temperature sensor o-ring? (I think it's BMW part number 13.62.1.743.299).
UPDATE: I measured a new FAE temperature sensor o-ring at 0.330" ID by 0.115" thick (i.e., 8mmIDx3mmThick).

The reason I ask is that most say the sensor (which controls the electrical fan in front of the radiator) rarely fails, so, in theory, can be re-used; but the o-ring often fails after removal ... (it hardens with age and also fails before removal).

Normally you'd just buy a new o-ring and swap the old temperature sensor out of the old lower radiator hose into the new radiator hose ... but I asked today at the dealership and they said BMW doesn't SELL the o-ring separately, even though we think we have the right part number

But it's just an o-ring (right?). The closest I can find that E46'ers have reported success with is the 79¢ "BrassCraft 0567" from Lowes; but it's not a perfect fit (it's a tad fatter than the original).

If we had the specification for the E39 o-ring, we could try to find a more suitable metric replacement.

A typical O-ring specification is something like:
- OFH O-ring spec = 7.0x2.5 (i.e., 7mm ID & 2.5mm thick)
- Oil Filter O-ring spec = 91x4 (i.e., 91 mm ID & 4mm thick)

I see another report of a working Buna N size from Lowes being 5/16" ID 9/16" OD and 1/8" thick, but, that was for an E46 and maybe the E39 is different. Another E46 thread lists the 8mm ID x 3mm cross section $1 Viton (high temp / coolant resistant) O-rings from Macro Rubber <www.macrorubber.com>as being more stable than Buna N .</www.macrorubber.com>

But maybe the E39 coolant temperature sensor o ring is a different size.

It would be best to make original measurements on a known good E39 temperature sensor; if you have a new (green) BMW coolant temperature sensor O-ring handy, would you please measure it for the team?

What is the ID and thickness of a new E39 coolant temp sensor O-ring?

REFERENCES:
- Coolant Temp Sensor O-Ring is a BMW Part Number
- DIY - Temp. sensor coolant leak repair
- E46 Cooling system temperature sensor part number
- Replacing the coolant temperature sensor DIY
- Recommended parts list for a cooling system overhaul
- E46 lower radiator hose coolant temperature sensor
- BrassCraft 0567 replacement for coolant temperature sensor o ring
- BrassCraft and Viton replacements for coolant temperature sensor o-ring
- Coolant temperature sensor o-ring dimensions
- Replace coolant temperature sensor o-ring with viton from macro rubber
- History of the o-Ring

194449 · Aug 1, 2010

You might as well buy a new sensor. They're cheap. FAE brand from Pelican comes with an O-ring. If you need an O-ring right now, you can get the ones mentioned from Lowes but be careful about the OD as well or you may end up not able to remove the sensor later, should you need to replace it (or the hose).

bluebee · Aug 1, 2010

pleiades said:
You might as well buy a new sensor. They're cheap.

I don't disagree. But, we should at least have the OPTION of buying just the O-ring should we want to re-use our old temperature sensors or if we want to fix a leak due to the old O-ring flattening on one side over time.

All I'm trying to do is find the right source and size to give us this option (as part of the complete cooling system overhaul parts list).

BTW, if it is BMW part number 13 62 1 743 299, then it's a $1.25 item that is available from the dealer since it's used for the air-temperature sensor as shown below (for my 2002 525i). That o-ring is 8mm ID and 3mm thick.

bluebee · Aug 5, 2010

pleiades said:
FAE brand from Pelican comes with an O-ring

I measured a new FAE temperature sensor o-ring at approximately (it's rubber) 0.330" ID (8.382mm) and 0.115" thick (2.921mm).

That means the best-fit is indeed most likely BMW PN 13 62 1 743 299 (which is for the air temperature sensor in the intake manifold) which is known to be 8mm ID x 3mm Thickness.

It's so hard to find this information (I don't think it was ever published on the E39 forums; because I found it only on the E46 forums), that I am glad we finally got this resolved.

bluebee · Aug 20, 2010

In a recent thread, cn90 mentioned that a constantly running auxiliary fan might be due to a bad lower hose coolant temperature sensor.

In that case, of course, you'd replace the old temperature sensor.

One question I have: If you do replace the temperature sensor, can the OLD one be jury rigged as a TEST tool for the temperature sensor?

That is, can we cut or open wires and at least get the two hot/cold end temperature set points in order to test whether the existing temperature sensor is good or bad?

I realize these things are inexpensive ... but I enjoy diagnosing more than just unthinkingly throwing parts at a problem.

Any thoughts on how to convert the old temperature sensor into a "test instrument" for the auxiliary fan circuit?

bluebee · Sep 11, 2010

bluebee said:
If you do replace the temperature sensor, can the OLD one be jury rigged as a TEST tool ... ... can we cut or open wires and at least get the two hot/cold end temperature set points

Nobody gave an answer to that ...

But I just ran into this thread which shows the importance of replacing the o-ring if you re-use your existing lower radiator hose coolant temperature sensor.

Also, you can see a similar experience in this thread and in this thread ... and in this BMW temperature sensor Q&A. (For a temporary fix, this post says to remove the old o-ring, wrap some teflon tape in the groove, and put the old o-ring back on.)

To summarize what they said, if your lower hose sensor leaks:
a) It could be the o-ring (they say it's a standard #31 o-ring)
b) It could be you didn't seat the temperature sensor properly
c) Or it could by you broke some of the fragile plastic when reinserting

Note: Can someone explain the sizing on the #31 o-ring which is 9/16 x 5/16 x 1/8 (considering the BMW o-ring is 8mm OD x 3mm thick)?

One caveat I'd mention is that the BMW Q&A above says to use Vaseline but any pool store will tell you to never use that on rubber o-rings (which pools have plenty of). They all say to buy the expensive pool stuff (which is said to not eat rubber).

If you know more about that topic ... (like where to get the pool lubricant cheap) ... please let me know!

Note: Pics below are from the aforementioned threads in case they go away in time.

carmanah · Oct 25, 2010

Thanks bluebee for digging into this.
It looks like the cheap $20 FAE sensor comes with a black o-ring, not green (Viton).
Q: before I run to the stealership for the o-ring part # you give, do you know if it is is Viton?

(Yes, this o-ring or sensor should be on anyone's coolant overhaul list. Three years ago I replaced everything, except this, and sure enough the old $1 o-ring leaked. So I wrapped it with teflon tape and shoved it back in. But now I have a slight loss going on and it looks like its this sensor again.)

bluebee · Oct 25, 2010

carmanah said:
before I run to the stealership for the o-ring part # you give, do you know if it is is Viton?

That's a great question.

I do not know if the exhaust sensor o-ring BMW P/N 13 62 1 743 299 is Viton or not.

I do see that my (brand new FAE sensor with o-ring) has a BLACK 0-ring, not green.

So I echo the question:
- How do we find what MATERIAL the BMW exhaust sensor o-ring is made of?

dvsgene said:
They are the same converting inches to mm BUt you have OD and ID reversed

You are smarter than I Gene!
I couldn't figure out why they had more numbers and why they didn't make any sense.

Thanks for deciphering that enigma for us!

If we keep digging, we'll have this o-ring thing all figured out for the next guy, who will benefit from all our efforts.

Acz4 · Oct 31, 2010

Looks like the o-ring has begun to leak on mine. I noticed a smell and recently noticed antifreeze on the under pan. I just took a look at it and I'm almost sure that is the problem. So you guys recommend replacing the sensor. I haven't had any problems with the sensor but I'd hate to use the wrong o-ring and have it crack that plastic.

Thank,
Andy

bluebee · Oct 31, 2010

Acz4 said:
So you guys recommend replacing the sensor.

I think the recommendation is to try to determine WHERE it's leaking and fix THAT!

- If it's the plastic area on the hose around the sensor opening, then replace the hose.
- Even if it's not the plastic around the hose, if the hose is old, replace it (and the entire cooling system).

- If your leak is somewhere on the sensor itself, then replace the sensor (which comes with a new o-ring).
- But most of the time, it's the o-ring, not the sensor or the hose, so, in that case, just replace the o-ring.

Again, if your cooling system is original, replace the entire cooling system (you generally can get away with not replacing the sensor but you MUST replace the o-ring).

Do us a favor whatever you do ... take a photograph of the old and the new and post the results here for us all to benefit.

bluebee · Nov 16, 2010

cn90, just today, found this nice $1.00 set of Brass-Craft o-rings that should fit the temperature sensor for anyone reading this thread in the future who can't find the BMW o-ring in stock.

ID = 5/16"
OD = 9/16"
Thickness = 1/8"

On the L side is new hardware-store O-ring (in Black), On the R side is the BMW broken O-ring (in Green):

gumbi4u · Nov 16, 2010

As much as I love these diy threads and info threads, there is way too much fuss and over all drama with this o-ring? Why is this such a big deal? Especially for a temp sensor o-ring? You find a ring that is similar or slightly bigger and it will do the job just fine. As far as material, its honestly does not matter as its not a "mission critical" item. Its really not a big deal. Its a rubber o-ring. Nothing more. Usually a fuel injector assortment will have the proper sizes.

bluebee · Nov 25, 2010

gumbi4u said:
way too much fuss and over all drama with this o-ring? Why is this such a big deal?

I think, once we know the size, it's not a big deal at all.

The problem "was" (no longer is) that people didn't realize their cooling system would leak because they re-used the temperature sensor and the temperature sensor o-ring.

Then, the problem was compounded when people had leaks but found BMW doesn't specifically sell that particular temperature sensor o-ring.

Since the o-ring must be replaced, yet, in the entire E39 forums the size was never listed (I know, I searched far and wide before I posted this thread), one didn't know what size to get. Compound that by the fact that the old o-ring was worn so it wasn't a good size reference; and then add the complication that it's a hot wet environment.

Anyway, now we know the size, in metric and SAE, and we have a whole slew of sources, from BMW themselves (manifold temperature sensor o-ring) to Home Depot (e.g., Brasscraft).

So, now it's not a big deal. But, before this thread, there was nowhere in the E39 forums the size listed.

BTW, here is what plieades had to say about the BrassCraft o-ring just today:
"The BrassCraft O-rings that have been mentioned elsewhere will work but they can also be a very tight fit, depending. I tried one on my existing sensor when I did my cooling system overhaul. (I thought I could use the existing sensor, but as others have experienced, the existing O-ring doesn't always seal when you insert the sensor into a new rad hose).

With the aftermarket O-ring, things were quite tough going back in (had to use some lubricant) and impossible in my case to get out when I wanted to install a new sensor (FAE) that came with its own O-ring."

Acz4 · Dec 11, 2010

I finally got the parts and replaced the sensor - I did order extra o-rings too. When I removed the original sensor the o-ring looked OK at first glance. I checked it and there was no damaged or nicks in it, just slightly flattened on the outer diameter.
After the replacement I started the car - no coolant leak

So that was the problem.

Brandon540/6M · Apr 24, 2011

Damn, I got fuxored by this today... I'm very happy to see this thread though! I actually knew from a high end replair place that you could just replace the o-ring, but I didn't know the model # and just winged it today and thought some liquid RTV would let me re-use the old o-ring without issue.. FAIL. Do not go that route...

I will be shopping for an o-ring tomorrow.. what was the final determined size from a hardware store again?

bluebee · Oct 3, 2011

Brandon540/6M said:
what was the final determined size from a hardware store again?

It's in the thread above (which is why nobody answered this).

BTW, today, someone in the E46 team (same engine as our E39 M54) accidentally put the intake manifold air temperature sensor into the lower hose coolant temperature sensor slot.

Predictably, it lasted only about 4 months before it blew out (causing grill damage) because it doesn't clip in the same.

Let's not make the same mistake!

Details here:
- E46 (1999 - 2006) > Damnit...I was driving and my air charge temp sensor "exploded"

Spikes007 said:
Ok so this morning (10minutes ago), I was going to work when all of a sudden I started smelling coolant. At first I thought it was the car in front of me, but a few seconds later a lot of white smoke were coming out of my hood...F**k. Because of the traffic, I had to drive for about another 1-2minutes to found a safe place to park. So anyway, I opened the hood. Coolant EVERYWHERE. It was obvious that it was coming from a hose and it wasn't a small leak. I start checking when I found that my air temp sensor (this) wasn't at its place anymore.

The sensor isn't damaged but the plastic grill around it is a little messed up. I have to buy a new one. But still, how the heck this can happen? I know I changed it about 4 months ago, but I don't remember how to put it. I mean is just sliding in the hole in the hose? I thought I had to turn it to lock it in position but it seems that it doesn't move. Anyway I am glade that I had premixed coolant in my trunk and it was only that, but still I want to know how this can happen. I was on idle so the pressure of the coolant should not have been that important to make it pop.

After 5 minutes I was back on the road and not even late for work.

ericono · Oct 16, 2011

Question, if I pull this sensor out does coolant continue running out the entire time the sensor is out (which would result in the need to add coolant and bleed the system, I assume), or does it stop flowing?

Thanks,

Eric

ericono · Oct 16, 2011

I answered my own question, after letting the car cool down I went ahead and pulled the sensor and coolant did not continue running out.

bluebee · Oct 29, 2011

Bearing in mine that the o-ring for the intake manifold temperature sensor is a part that 'can' be ordered, here is a picture of the intake manifold temperature sensor location on the 528i from this thread:
- Detailed DIY for Crankcase Ventilation Valve Overhaul for the M52TU Motor

TeeDubya · Dec 17, 2011

Inexpensive solution

I just put a -011 buna o-ring underneath the green Viton worn out-o-ring. It lifts it up and doesn't allow it to flatten out so much. It's working fine. A -011 has about the same ID per the chart here:
http://www.marcorubber.com/sizingchart.htm

You can get size -011 anywhere including this kit at Harbor Freight of 180 Viton o-rings for $19.99
http://www.harborfreight.com/180-piece-viton-o-ring-kit-67525.html

bluebee · Jan 25, 2012

People are still looking for the aux sensor O ring apparently:
- E39 (1997 - 2003) > Cooling ovehaul - source of a sensor o-ring?

And, they're still getting the wrong answers mixed in with the right and new answers ... sigh ...

ARX3 said:
I'm looking for part number of the green o-ring that goes on the temperature sensor (13 62 1 433 077). Dealer says I need to replace the entire sensor at $40... Doesn't seem to make sense. Has anyone found a source of the correct size o-ring

oembimmerparts said:
bmw only sells it with the sensor, If you take the old one into a napa or other parts store you can match it up with one of the ones they have.

joebox said:
I would just replace the sensor. It will not be possible to get an EXACT match for that o-ring, and the result will be a leak from the coolant temp sensor housing. I found this out out the hard way a few years back. My parts guy at the dealer parts counter told me this, but I did not listen. Turns out he was right.

bmw_n00b13 said:
I can't see why it'd be impossible to find an exact match to an O-Ring….it's not like they're rare.

jonamatt said:
Found a good source for the O-ring. It is a standard AS568-203 size, found them at www.oringwarehouse.com for 5 cents a piece.

vatoman said:
BMW PN 13621743299 worked for me no problems since replacing and I have a spare in trunk just in case.

Read this for further proof
http://www.bimmerfest.com/forums/showthread.php?p=4182085&highlight=#post4182085

bcbp14 said:
I used Danco #33 orings to hold me over untill my sensor arrived. When I tried to pull the old sensor out it would not budge, it must have expanded. I had to remove the lower radiator hose and push from the inside, even then it was a struggle.

blz456 said:
Ordered mine from ecs tuning.

coopster530 · Jan 30, 2012

Temp sensor O-ring

Hiya Bluebee.

FWIW, I'm currently doing the cooling system and other things, and noticed today that the sensor I bought has the green oring. Now I forget, but I know it came from probably Pelican (or maybe Bavarian).

bluebee · Feb 4, 2012

coopster530 said:
noticed today that the sensor I bought has the green oring

Here's the M54 engine coolant temperature sensor from this new DIY today:
- The Best of Bimmerfest! > Do-It-Yourself H.Q. > DIY: Water Pump, Thermostat, Hoses & Coolant Flush : X5 3.0 Auto

bluebee · Feb 28, 2012

For the cross-linked record, this somewhat predictable experience posted today illustrates why the o-ring matters:
> E39 (1997 - 2003) > Coolant Temperature sensor

willow creek said:
I just completed my coolant system overhaul on our '02 530i. The only problem I ran into was a leak at the coolant temperature sensor. Coolant was leaking from around the sensor. Come to find out it's fit was not tight in the new lower hose. I ended up putting back on the old hose and the leak stopped. I cannot decide if the opening in the hose for the sensor is defective, the o ring is worn, or the the sensor and o ring need to be replaced. Has anyone else had this problem?

bcbp14 · Feb 28, 2012

I should probably ad that I would have just left the Danco o ring in there as it was a much tighter fit. So tight in fact that I destroyed my old sensor in the removal process an nearly destroyed my new lower radiator hose. The Danco ring must have expanded in the housing.

bigjoe87865 · Mar 6, 2012

Just wanted to say, I was able to purchase the OEM o-ring at my local dealer... they said it is a common item they sell.

$1.80 a pop.

Trebbia · Apr 9, 2012

bigjoe87865 said:
Just wanted to say, I was able to purchase the OEM o-ring at my local dealer... they said it is a common item they sell

When I had called my dealer, they said that I could only get the entire sensor.

The oring (they said) wasn't sold seperately (which is confirmed by realoem).

Point is that you probably bought the air-sensor o ring, which IS sold separately!

champaign777 said:
the o-ring winch is 1 to 1 to coolant temperature sensor o-ring is

04 O-ring 8X3 1 13621743299 $1.25

+1

champaign777 · Apr 9, 2012

the o-ring winch is 1 to 1 to coolant temperature sensor o-ring is

04 O-ring 8X3 1 13621743299 $1.25

this o-ring is from Temperature sensor air but it's 100% the same part as on coolant temperature sensor
( my start to leak and this how i found it so i just used my old O-ring 13621743299 on a coolant temperature sensor and it match perfect )

danzee · Nov 10, 2012

Confirming that 9/16 x 5/16 x 1/8 works fine

This o-ring from the hardware store worked perfectly for me. I lubricated it with antifreeze solution (50-50) and it went in without a problem. No leaks after test rides.
FWIW, the green one I took out measured 0.331 ID and 0.112 Thk.

bluebee · Aug 5, 2013

For the record, QSilver7 today posted a good description of what makes the electrical aux fan kick in, based on the thermoswitch in the lower radiator hose:

QSilver7 said:
If the DIY is for a 3/5/7 series built before 9/98...the confusion may be the results of reading a DIY that doesn't apply to your e39. The aux fan in the M52TU/M54/M62TU engines don't use a relay...it uses a PWM signal from the DME to an output final stage in the aux fan to turn it on/off.

bluebee · Jan 31, 2014

This question came up again today ...
> E39 (1997 - 2003) > 528i wagon leaking coolant from radiator lower hose sensor?

Sinful said:
Hi,

I just noticed a small leak from a sensor thats on the lower radiator hose. It's coming from a small orifice off the body of the sensor or maybe the adapter? Would that also explain why the temp guage needle is acting up?

See also:
- What is the proper coolant level bobber stick height (1) & what to do when your expansion tank coolant level sensor float bobber stick is MIA missing in action (1) & where to find leaks when the CHECK COOLANT LEVEL is lit on the instrument cluster (1) & where does the coolant level sensor cable go (1) & what is the o-ring size for the coolant level sensor (1) & what is the temperature of the coolant when the thermostat opens under normal conditions (1) & how to modify the cooling system expansion tank 2 bar cap to 1.2 bar to vent at a lower pressure (1) & how to retrofit a coolant level sensor to an E39 that doesn't have it (1) & what is the most often recommended coolant (1) & tricks for efficient flushing (1) bleeding (1) and a coolant refilling DIY (1) & some behr/hella cooling system autopsy photos (1)

bluebee · Aug 13, 2014

For the crosslinked record, see also:
> E39 (1997 - 2003) > Water Sensor O-Ring Fix

yoshi900 said:
Ah! Thanks CN90 for the link. I must have been searching in the wrong forum or used the wrong keyword.

bluebee said:
I found this thread while searching for all the o-rings in the E39.

In the future, when looking for any E39 0-ring, just go here:
> E39 (1997 - 2003) > Complete list of all o-rings (by size & by part number) to buy when ordering parts

That thread notes that the the lower radiator hose o-ring is the same size and material as the intake manifold air temperature sensor o-ring.
- O-ring 8X3 1 13621743299 $1.25
- Cooling system lower radiator hose aux thermoswitch sensor o-ring
- intake manifold air temperature sensor o-ring.

http://realoem.com/bmw/showparts.do?model=DT43&mospid=47584&btnr=11_2879&hg=11&fg=40

bluebee · Dec 25, 2014

Looks like the 3-series team has the same questions today that we've already answered ...
> E46 (1999 - 2006) > Lower Rad hose sensor?

OscarN said:
Hey guys! Woke up this morning to a small coolant leak. However it isn't the hose that is leaking, it's the sensor. (See picture below) Does anyone know the part number? Or where I can buy it?

SilberVogel said:
Part number for that o-ring is 13621743299 (same o-ring found on the IAT sensor). Definitely a common leak and have even seen some use teflon tape as a temporary fix if it's leaking badly.

aftermath said:
Brass craft 0567 for the oring itself. Got it at lowes for 79 cents. just changed mine yesterday. Haven't checked it since I replaced hopefully it's working...found it on another thread somewhere on here.

ahull said:
Adding .02 here: I'm not sure how well the plumbing rubber will hold up over time as it's not designed for exposure to coolant or the wider range in temperature variation it will see in the lower hose (should be the coolest point of the system but it's still probably hotter than a hot water tap in the house). But for a short-term fix it should do just fine.

micosan · Jan 19, 2015

Bluebee
Thanks for this thread and many others. I just replaced the o-ring and fits well for my car. 2007, 550i, Sports Pkg, Prod. Date 11/2006, 87K miles:thumbup:

cn90 · Jan 28, 2017

My update.

My 2006 X5 3.0 M54 Temp Sensor O-ring leaks only when COLD.

Most hardware stores carry O-ring 9/16 x 5/16 x 1/8 = 14.3 x 7.937 x 3.175 mm.
(I think BMW o-ring is 8mm ID x 3mm thick; or 14mm OD).

It is the extra thickness that makes the hardware store O-ring a better fit.

Tricks as mentioned:

1. I used a bit of grease to help insert it.

2. As long as you don't remove the reservoir cap, coolant loss is minimal, but make sure you check coolant level once you are done. And check it again a week later.

3. Wash the area with some water so later on, if you have a leak, you can spot it.

4. The sensor only fits one way (the vertical ridge on the sensor faces forward). It is a bit stiff, so LEFT hand below the rad hose to support it, while using the RIGHT hand (squeeze the side tabs) to insert the sensor. You will hear a "click" once it is in. Gently tug it up to be sure it does not come out. Some people didn't install properly (not seated properly), that was why it leaked.

That is it...

Next person to replace coolant temperature sensor: Please measure the O-ring size!

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