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

TeeDubya · Dec 17, 2011

Inexpensive solution

bluebee said:
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

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.

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 )

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

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...

cn90 · Dec 8, 2018

Update on hardware store O-ring.

- As mentioned above, the Danco #31 O-ring is the ticket. It is a tiny bit thicker than factory O-ring and the Danco O-ring is a perfect fit, but only on BMW OEM Lower Radiator Hose (avoid Gates or other aftermarket hoses!).

- The space is tight, so when you install the sensor back, squeeze the side tabs and insert it (lubricate the O-ring with grease or coolant). Once done, use your fingernail to feel it: the OEM sensor edge (RED arrow) should be about 1 mm above the housing (YELLOW arrow).

- The tabs must be in the YELLOW Circle. From above it is very difficult to tell if the tabs are in the slot, you may have to use a mirror to look. But the step above (sensor is approx. 1 mm above housing) is good enough.

- An of course, use paper towel to clean around that area really dry, this way if you have a leak later, it is easy to detect.

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

TeeDubya

bluebee

coopster530

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