4.8 expansion tank - level sensor leak

[svvg]

Grateful for some advice please. I’ve got a 2004 e53 x5 - with a 4.8 n62 engine. 108,000 miles. I’m losing coolant - topped up 1.5 litres yesterday and it’s all gone today.

First thought was the valley pan gasket transfer pipe, but upon closer inspection it’s coming out of the base of the expansion tank (yep. Lucky bstrd....) - I think from where the level sensor fits. The tank’s empty down to the level of the sensor (as residual fluid left in the base of the tank....) - and when I removed it to check, was really surprised that there’s no o-ring on the sensor? - So am not sure how it’s supposed to seal?

Anyone know anything about this? Is there supposed to be an o-ring? Real oem doesn’t show an o-ring on the part...

Or have I got a bigger issue with too much pressure building up and it’s pushing it past the sensor (which might otherwise be capable of sealing perfectly....).

Many thanks!!

[svvg]

RealOEM.com - Online BMW Parts Catalog

[crystalworks]

I don't believe there is a seal for that sensor and there should not be any coolant in there. I think that sensor reads a magnet on a float inside the tank. You might have a crack in the tank in the sensor recess, especially if that is the original tank. They last 80k to 100k miles typically. I have a new tank here I can verify on. Will get back.

[740ilDuke]

There is no seal on most of them, it seals by tension.

Most new tanks come with the sensor, so I would replace the tank and the associated lines to it for good measure.

You can try replacing the sensor, it's $10.

Ive been buying from Max for years, fast shipping and great support. He does his research on what he carries and often has a few options.

https://www.oembimmerparts.com/BMW-E...rts-s/1869.htm

[svvg]

Thanks very much guys. If I replace the tank do you reckon I should also replace the sensor? - to ensure a snug fit?

[cn90]

- The level sensor sits in a dry well.

- You have a leaking reservoir. Replace using ONLY BMW reservoir. Any other brand is potential problem in 2019! Behr reservoir is probably made in China etc.

Use only BMW brand.

[crystalworks]

Originally Posted by cn90

- Ten level sensor sits in a dry well.

- You have a leaking reservoir.

That's what I was trying to say... Rather poorly. Hah! Words are hard.

[svvg]

Yep. Understood - do i also get a new sensor - as it seems to be an integral part of how it seals...?

[740ilDuke]

Yes, if you replace the tank, replace the sensor.

Originally Posted by svvg

Yep. Understood - do i also get a new sensor - as it seems to be an integral part of how it seals...?

[svvg]

Originally Posted by svvg

Yep. Understood - do i also get a new sensor - as it seems to be an integral part of how it seals...?

Just realised what you’re all getting at... i.e. the place where the sensor fits into is a separate chamber - not an entry point into the fluid containing part of the reservoir - hence if it’s leaking from the reeservoir, then it’s because the tank’s knackered/cracked into that chamber...

Thanks a lot for the responses. Impressive knowledge on a relatively random part!