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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 07-24-2009, 11:58 PM
jcourcoul jcourcoul is offline
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DIY - Temp. sensor coolant leak repair

Have you noticed that the coolant level seems to slowly drop but all the hoses look clean and dry? You may be suffering a small leak in the temperature sensor located in the lower left radiator hose. This sensor uses an O-ring that can shrink and harden with age, allowing small amounts of coolant to ooze when the engine is hot and the radiator is under pressure, but the amount evaporates or blows off, without leaving much of a trace. In this DIY, we'll see how to replace the part to neutralize the leak. No tools are needed and the only part you have to get is a new sensor, P/N 13621433077, $32 MSRP, can be found in the market in the $17-$40 range. You may be able to get a replacement O-ring and change only that for less. As a side note, this sensor is used to control the electrical fan in front of the radiator to maintain coolant temperature.

First off, let the car be totally and absolutely cold. Do the repair next morning. Not only you won't be scalded, but you will lose a lot less coolant. If you were planning on flushing the cooland as regular maintenance, you can go ahead and drain the old coolant now, but you can change the sensor without doing that.If you are not flushing the old coolant at this time, make sure the pressure cap on the expansion tank is screwed on tight; do not remove it. The sensor location is shown in pic. #1, you may see a slight ooze on the pressure relief holes on both sides.

You are replacing the old sensor, #2, with a new one, #3. Note how the new O-ring is much rounder. Sensor is held in place by the two side tabs. If you're doing a "live exchange" (no flush), you can make the new sensor slide in easier by pre-lubeing the O-ring with undiluted BMW coolant.

The connector needs to be removed first, the sensor cannot be removed otherwise. As shown in #4, pull out and hold the chrome retaining clip and pull the connector straight up. If it resists, that means you are not pulling the clip out enough.

Now comes the quick part if you don't want to lose too much coolant. Place the new sensor in an easy and quick to reach location. As shown in #5, pinch the two side tabs on the old sensor together and pull gently but firmly straight up. The old sensor may be somewhat stuck in there, but do not go Neanderthal on it cause the hose fitting can be damaged and then you'll have much bigger problems. When it releases, quickly pull it out, set aside, grab the new sensor and slide it in until it clicks in place, noting that it is keyed. Don't overdo the pressure for the same reason as before.

Before reconnecting, I like to daub a smidge of dielectric grease on all my connectors to keep the moisture out and to ease the next disconnect, #6. Just press on till the retaining clip clicks on. Now unscrew the pressure cap on the expansion tank and fill up the missing coolant. Giv'er a whirl to get everything nice, hot and pressurized, to make sure the leak is fixed? Time for a beer or whatever fluid suits your fancy after this extenuating repair job?

Next time around, you could change the O-ring on the old sensor you removed, use that and save a bit.
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Last edited by jcourcoul; 07-25-2009 at 01:01 AM.
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  #2  
Old 07-25-2009, 02:59 AM
e46_platform e46_platform is offline
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Originally Posted by jcourcoul View Post
You may be able to get a replacement O-ring and change only that for less.
true.
this less than a dollar solution works for me

http://www.bimmerfest.com/forums/sho...t=#post4182085
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  #3  
Old 07-25-2009, 10:40 AM
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No signs of this on my e46 yet (only 28k miles) but will squirrel this away for the future.

Thanks for taking the time to wrote this up and take pics.
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Old 07-26-2009, 08:59 PM
happypanda happypanda is offline
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I have had a similar problem with my E36. Do you know if this also applies to this model?
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  #5  
Old 07-27-2009, 12:10 AM
jcourcoul jcourcoul is offline
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Originally Posted by happypanda View Post
I have had a similar problem with my E36. Do you know if this also applies to this model?
Not familiar with those models. However, if you have something that looks similar and/or the diagrams on RealOEM.com also look similar, the failure would be the same: a shrunken, hardened O-ring that can't take the pressure anymore. And the repair would be likewise, but I wouldn't know the specific details such as part no's.
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Old 07-27-2009, 04:54 AM
sierrakilo99 sierrakilo99 is offline
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This is good info. Should probably add this to the list of parts to replace (the o-ring) when doing the coolant system overhaul later in the car's life.
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Old 10-23-2009, 06:18 PM
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Coolant Sensor Leak

After replacing my lower radiator hose only to find the leak was coming from the coolant sensor, I went out and got a 10 pack of VITON (high temp / coolant resistant) O-rings from Macro Rubber . They were only $10 for the 10 pack. I believe Viton may be a more stable rubber compound than Buna N for this fairly challenging O-ring application. Needs to withstand hot, cold, vibration and chemicals. The VITON O-ring is a 8mm ID x 3mm cross section. Better than the $40 sensor from BMW and just as effective if your sensor works, but is leaking.
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Old 10-23-2009, 08:36 PM
jcourcoul jcourcoul is offline
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Quote:
Originally Posted by db123 View Post
After replacing my lower radiator hose only to find the leak was coming from the coolant sensor, I went out and got a 10 pack of VITON (high temp / coolant resistant) O-rings from Macro Rubber (www.macrorubber.com).
Web address does not exist ("this domain is for sale"). Part no. would be useful, cause the idea here was that the O-ring was some custom size not readily available, so your input is quite good news.
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Old 10-24-2009, 06:48 PM
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Very good to see - If a working link and part number can be confirmed, it should be wiki-fied.

I Iended up RTV-ing my sensor back in. Dang dealer parts desks around here are not open on Saturdays or Sundays, and I needed the car back on the road. I went to NAPA to see what they had as far as suitable oRings. There was one fuel injector oRing that was maybe an 8mmx4mm. That was the closest, but it was too fat for the bung on the lower hose......
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  #10  
Old 10-24-2009, 08:13 PM
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I remember seeing this thread months ago and I was happy to see it was in the wiki. I just did this yesterday because coolant was leaking pretty bad from there on my car. Oddly the O-ring looks fine on the old sensor but replacing the sensor seems to have stopped the leak. Good write up!
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  #11  
Old 10-24-2009, 08:15 PM
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Hmm, I'll check mine as well because I have to put a tiny bit of coolant in every week. Thanks for the write up!
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Old 12-01-2009, 08:27 PM
bshade1 bshade1 is offline
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Looks like I have this very problem. Thanks for the detailed directions and advice on what to do. One question though. If I take the sensor off, replace the O Ring, and reinstall, how much coolant can I expect to leak out in that timeframe? I figured since it is at the bottom radiator hose that gravity might force it out. Can I plug it somehow while I change the O Ring ya think?
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Old 12-02-2009, 01:04 AM
jcourcoul jcourcoul is offline
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If the car is stone cold and the caps (pressure/bleeder) are shut tight on the expansion tank, very little BMW joy juice will leak out, mere droplets. Of course, provided you don't go about squeezing the hoses...
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Old 12-02-2009, 07:32 AM
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I loose a small amount of coolant over time and havent been able to figure out where its going. I'll give this area a closer look.

Here is a link that gives the BMW part number for just the o-ring.

http://www.bimmerfest.com/forums/sho...p+sensor+rings
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Old 12-02-2009, 04:57 PM
bshade1 bshade1 is offline
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I'd like to thank jcourcoul for the perfect insturctions on how to fix this problem. And also E46-platform for giving the specs on the o-ring. Cost me $2 for a 10pk. and although it was a bit more difficult to push the sensor back in i just ran it for 20 minutes and not one drip (used to drip right out of the gate). Word of advice, since that o ring is a bit thicker and thus harder to push the sensor in, I suggest grabbing the bottom of the hose connection with your fingers and pushing down on the sensor with your palm. In fact squeexing it on there. Pushing straight down with too much force may damage that connection (I think anyway).

Thanks gain. So far with this site I have fixed this issue for $2 (20 cents effectively)and a tailight issue for $1. I'm a fairly new BMW owner (1 year) and had an older Honda prior. I worked on it whenever needed. I must admit this thing intimidated me at first, but so far so good.
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Old 12-02-2009, 05:07 PM
jcourcoul jcourcoul is offline
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You did prelube the whole tip of the sensor with undiluted antifreeze? Remember Orlando Bloom's immortal words in Evolution: "There's ALWAYS time for lubricant!"
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Old 12-02-2009, 05:12 PM
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Quote:
Originally Posted by jcourcoul View Post
You did prelube the whole tip of the sensor with undiluted antifreeze? Remember Orlando Bloom's immortal words in Evolution: "There's ALWAYS time for lubricant!"
When you're doing a "live exchange" (I had to do this DIY not more than a week ago!) you'll have a stream of antifreeze that will lube it as you push it in.

The whole process took me about 30 seconds (then another 3 mins to top off the coolant ).
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Old 09-10-2010, 09:28 PM
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Quote:
Originally Posted by jcourcoul View Post
You did prelube the whole tip of the sensor with undiluted antifreeze?
On July 7th, 2010, BavAuto says to use Vaseline but any pool store would say to use Teflon-based o-ring lubricants ...

To find a good source of the lubricant, I opened a thread on the o-ring lubricants over here today.

BMW E46 Lower Radiator Hose Leak at Temperature Sensor – M54 – E39 X5 X3 Z4 Z3


July 7th, 2010
Q
Replaced a bunch of parts, one is the lower radiator hose when doing a belt replacenment. It is leaking at the sensor connector. Replaced the sensor and it is still leaking with new. Here is a reply from Mike at BMW CCA. Do you have some additional recommends? “The new style hoses have a plastic quick disconnect mechanism that uses an o-ring seal. This was in response to the fact that the engine compartments are incredibly tight nowadays, and there’s no room to get in there with a hose clamp tool. Of course, the new style means it’s easy to break the brittle plastic and you have to think about the o-rings. Anytime you see an o-ring, you should take it off, inspect it for cracks or deterioration under a light, and if none is found, lubricate it with Vaseline before reinstalling. If the o-ring breaks when you take it off, it needed to be replaced anyway. I doubt the problem is the hose itself. I would say the connector is either not snapped in completely, the o-ring is shot, or the plastic is cracked..

A
I have a new hose and the temp sensor, here at my desk. All appears to be as I would expect. This is actually a fairly common issue when either the hose or the sensor are replaced, on the M54 engine applications. The o-ring compresses adequately as the sensor is installed in the plastic fitting at the hose end. During actual installation, I would lubricate the o-ring with some Vaseline. I agree with Mike, that the sensor is likely either not plugged in fully or that the o-ring is not seated properly or is damaged. Remove it one more time, inspect the o-ring, if it’s OK, lube it and re-install. Make sure that both snap clips are fully engaged. Please let us know what you find.






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  #19  
Old 09-13-2010, 07:38 AM
Starless Starless is offline
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Completed the DIY succesfully. Just the O-ring (BMW part # 13621743299), not the sensor itself. I was impatient to wait for the car to get completely cold (like in the morning), so I went for it and lost may be half a cup of coolant (was not too bad but had to wipe it off of the garage floor). The old o-ring was toast - flat and hardened. Hopefully it will stop my little mysterious coolant leak

Last edited by Starless; 09-13-2010 at 11:11 AM.
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Old 12-02-2009, 05:21 PM
jcourcoul jcourcoul is offline
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Nothing like natural lubrication to make the process more memorable. Too bad it's over so quickly you almost don't have time to enjoy it. Almost....
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Old 12-02-2009, 07:07 PM
bshade1 bshade1 is offline
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I am uncomfortable with the word "lube" being thrown around so much. But yes, I did. Just went out and checked under the car and nada. Woohoo!!!
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Old 08-03-2012, 10:59 PM
GoForthFast GoForthFast is offline
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I am uncomfortable with the word "lube" being thrown around so much.
That is all so very interesting. Just exactly what previousl experiences in your distant background makes you so sensitive to "lube"?
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Old 12-03-2009, 04:50 AM
TenzoR TenzoR is offline
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I just followed this guide and something I noticed differently about my car. The metal clip holding the sensor wire had to be pushed towards the front of the car (like a retention spring almost) and the wire easily slide out. On the 4th picture, it showed the clip being pulled towards the rear of the car, which I tried and didn't work. Else everything was straight forward
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Old 12-31-2009, 07:17 AM
mikelebet mikelebet is offline
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Hi all - outstanding thread!! Did mine the other day and everything was very smooth. No more leaks, nice and simple. Appreciate all the help!
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  #25  
Old 07-31-2010, 10:57 PM
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bluebee bluebee is offline
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What are the ID and thicknes dimensions of the coolant temperature sensor o ring?

I opened a thread on the E39 side asking for someone to measure the ID and thickness of their coolant temperature sensor green o-ring ... but maybe we can team up to find the answer to these questions:

Are we sure the the right material is BUNA N (or is it Viton)?
Are we correct in the part number being 13.62.1.743.299?
Is the correct size of the original o-ring 8.0x3.0 (8mm ID, 3mm thickness)?



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
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