Leaking temperature sensor on 330?

[Manolito]

This appears to be the source of the water leak.

Anyone else had one of these fail and start leaking?

How does it come off the radiator?

I gotta finish the water pump job on the 328 so I can use the ramps to get the 330 up so I can see how it goes together.

[Manolito]

On further inspection, no ramps are necessary. It just pulls out with a thumb release. If I leave the radiator cap on, no water comes out when I remove it.

It is solid metal up to the O-ring, so the O-ring must be leaking. It seems a bit too easy to slide it in, so the O-ring is not a very tight fit. I will see if I can find a fatter O-ring for it. If I do, I will post the part # of the O-ring that fits so others can correct this problem.

[fourdoorfanatic]

super super common. i'm not sure why they put the fan temp sensor in the hose now rather than the side of the radiator, those almost never leaked.

[Manolito]

The O-ring from a fuel injector is almost perfect. Same ID, slightly larger cross-section. Just a bit too tight. If I were willing to tap it down in the hole with a stick, I could probably have forced it in.

I would have wrapped some teflon tape around the original O-ring and put it back in, but I tore it getting it off to try the fuel injector O-ring, so I was screwed.

I looked all over town for an O-ring to fit it. No luck.

Finally ended up at the BMW dealer. The parts man is a comedian. "I can sell you that O-ring for $40, and it comes with a free temperature sensor!"

Original O-ring
ID: 8.2mm
Cross Section (radial) 2.6mm
Cross Section (vertical) 3.2mm
OD: 13.4mm
This is 5 years old, so it has flattened a little, and cross section may have shrunk a bit, ID may have stretched when I removed it.

Fuel Injector O-ring
ID: 8.0mm
Cross Section 3.5mm
OD 15.1 mm
This is just a bit too fat to fit.

Groove where O-ring rests is about 8.5mm DIA and 3.8 mm wide.

If I find an O-ring that fits. I will post the source and part #. It has to be cheaper than $40 for a new sensor ($16 on line for FAE brand).

[fourdoorfanatic]

any luck yet? i went through every o ring in the shop i work for and couldn't find one to fit. injector o rings were the closest i could get, and like you said they were a little too fat. let us know!

[Manolito]

I just ordered a five-pack of silicon rubber O-rings from SmallParts.com

Will put one on the old sensor and put it in when they arrive, and will report back after a few days.

I suspect that it may not fit because on other sites, O-rings that list as being 1/8" cross section are actually bigger than 1/8" if you look at the listed size in mm. SmallParts.com just lists it as 1/8" and does not list the size in mm. I thought about calling them to ask, but decided to roll the dice.

[Manolito]

Nope, too big. Part of problem is that I mis-read my caliper originally. I just went back up and corrected the O-ring measurements in post above. Also, 1/8" thickness O-rings are actually bigger than 1/8" as I suspected. I will keep trying.

[caleb27]

I don't think its too hard to get to. May be an o-ring as well.

[fourdoorfanatic]

...uh huh. any luck yet manolito?

[Manolito]

I think have searched every size chart on the web. Standard inch-unit sizes will not fit, not even the military or aerospace specs.

That leaves us with metric O-rings.

I think that the original was a M3x8
The Bosch fuel injector O-ring is an M3.5x8

So the choice is -
1) Buy M3x8 and replace it if/when it shrinks like the original did.
2) Find a very soft (softer than #70) M3.5x8 and force it in.

I have not yet found anyone who sells O-rings in small numbers retail who stocks either of the above sizes.
O-ring selections that are available in kits don't include either if these sizes.

I have sent out a few emails, but for a small lot like I would be buying, I doubt that any vendors will respond.

[fourdoorfanatic]

yeah, we (the shop i work at) have been having to sell the entire sensor. its just stupid they use such oddball sizes for things. its like the ecm i had in my m3, it had a bad resistor or something, i can't remember what now, but for the life of me the specs were so weird on the peice that i had to give up on finding one and get a remanned unit.

[Manolito]

The only response I got from vendors was:

Allied Metrics Seals & Fasteners, Inc [alliedmetrics@nac.net]

Says they will sell M3x8 Viton O-rings
Pack of 100 for $85

I am not willing to spend $85 to try one out. If I was sure they would work well, I might try buying 100 and then post an ad offering to sell them to other e46 owners who sent me stamped self-addressed envelopes so I could recover my $$.

[fourdoorfanatic]

no joke, thats double the list on the sensor. i couldn't even make that up in labor if i bought the lot of em at the shop. bump that.