Coolant Leak at Lower Radiator Hose Temp Sensor
 

I have a 2006 3.0i. I discovered I have a small leak that appears to be coming from the temp sensor on the lower radiator hose. After looking on line at the part it looks like it can be removed and it has an O ring. I suspect the O ring has hardened. It looks like it can just be removed, a new O ring installed and the sensor reinstalled. Anyone have to do this? Were you successful or did the sensor plastic break or fall apart? I had that happen with the trans cooler thermostat.

If it's a part that's likely to break I'd rather just go ahead and order a new one as if it breaks my car will be down until I can get a new one and I need it for work. I don't know if the hose has ever been replaced as the records are incomplete. The hose looks and feels in good shape. If I go ahead and order the sensor I'll probably order a new hose as well.

Thanks in advance!

Leaky o-ring. I just wrapped mine with Teflon

The o-ring is easy to change and will not be that hard. It is available separately from the sensor. There is a chance that part of the problem is that the plastic housing portion that it sits in is slightly warped though as well. The teflon, as andrewwynn suggested, works well and is really quick as you don't even need to remove any coolant if you let the car cool down and don't take off the cap.

I replaced that o-ring, along with the lower radiator hose (and a bunch of other stuff) recently on my '01 3.0i with 186k miles, and there were no problems. Plastic things un-snapped like they were supposed to, etc.

And BTW, my existing o-ring was fine, nothing leaking, but I put the new one in anyway. As with all those o-ring fittings, a little silicone grease or lubricant will help it seat better, which will help things seal better.

Well, I'll say I did not try it with the car cooled down and the cap still on. Pretty cool if that is enough to keep the coolant from coming out. :thumbup:

Thanks guys. I'm getting a new o ring. Hose looks to be in good shape. I'm going to try doing it when cold with the cap on to see if 80stech trick works. It will be great if it does.

Same leak happened when I was changing all my coolant hoses. It didn't leak before I unplugged it, so unplugging it broke whatever deal was keeping it from leaking: the o-ring was cut. I couldn't find it sold separately, so I got a whole new sensor (from FCP Euro I think) which wasn't that expensive.

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I use the 50-cent O-ring from hardware store.
It works fine.

Detail in here:

https://www.bimmerforums.com/forum/s...g-for-59-cents

Same happened to me a few months ago - 2006 3.0i with 110.000miles.


New o-ring fixes it, no coolant drainage if you work on a "cold" car with the expansion tank cap in place.


Bought the O-ring: 8x3mm - fits perfectly.


It's a nice & easy job to do...

I checked my notes, and here's the o-ring I bought when I replaced that lower radiator hose:
https://www.rmeuropean.com/Products/...0-MFG1190.aspx

Calls itself 8x14, which is 8mm ID, 14mm OD, 3-mm thickness