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Old 11-14-2012, 01:46 AM   #9
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Join Date: Sep 2008
Location: Fort Smith, Arkansas
Posts: 236
My Ride: 1999 328i 4dr
Originally Posted by jfoj View Post
Likely your problem is the temp sensor O-ring in the lower radiator hose. Very common problem, even if it is not leak, it needs to be replaced. No tools needed, very little coolant lost as system vacuum keeps coolant from leaking.

Technically the O-ring is not a serviceable part.

See my signature for the O-ring part number.

In a pinch, you can pull sensor, remove O-ring, 4-5 wraps of teflon tape in O-ring groove, reinstall.

If the switch is wet at all or if there is any wetness on the lower engine cover it is leaking.

Other than that, expansion tank is a likely suspect.
Great thread guys....I know my o-ring is leaking, I can see fluid around it.
I have a new o-ring already but when the sensor is removed does fluid pour out?
Dont want to drain my rad just yet. I'm pretty sure my expansion tank is also leaking to up by
the top of the rad. Light is coming on and can see fluid around exp tank connections area.

1999 328i E46 with a M52TU - 2002 X5 E53 3.0i with a M54 - -

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