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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 05-02-2015, 06:45 AM
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540iman 540iman is offline
resident, old fart
Location: N.W. Indiana
 
Join Date: Sep 2008
Posts: 1,789
Mein Auto: 2002 540i sport
Question about "no O-ring" for coolant level sensor.

When I went to finish my water pump DIY on my 2002 540, I was surprised again (done this job on other 540s) that there was no O-ring for the level sensor at the very bottom of the expansion tank. I looked for quite a while for a left-over O-ring amongst my left over parts to go back on the car and I found there was none left behind on the expansion tank or the sensor. The sensor just seems to twist onto the bottom with a snug fit, but no seal which I expected to find. Real oem does not show an O-ring for this connection either. Appears just plastic against plastic. I just can't wrap my head around this. Is there supposed to be an O-ring here?
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  #2  
Old 05-02-2015, 08:05 AM
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TheHockeytowner TheHockeytowner is offline
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Location: Ypsilanti, MI
 
Join Date: Nov 2010
Posts: 230
Mein Auto: 2003 525i
Correct me if I'm wrong, but the level sensor does not actually contact the inside of the expansion tank. There is space molded into the bottom of the expansion tank that the sensor sits in, and the float inside of the tank triggers the level sensor by some effect (Hall? Voodoo?).
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Old 05-02-2015, 08:50 AM
JimLev JimLev is offline
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Location: MA
 
Join Date: Dec 2003
Posts: 4,164
Mein Auto: 540/6, S60 Volvo, Tribeca
Correct, it's not in the tank with the coolant.
The sensor is a reed relay (switch) that is activated by magnet on the float stick inside the tank.
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Old 05-02-2015, 10:32 AM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K
Here's a closeup picture of my expansion tank level sensor (more in the threads below):
- Behr radiator and Behr expansion (aka surge) tank autopsy (1) (2) & request for another autopsy (1)
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See also: E39 Bestlinks & How to easily find what you need
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Old 05-02-2015, 02:18 PM
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540iman 540iman is offline
resident, old fart
Location: N.W. Indiana
 
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Mein Auto: 2002 540i sport
Quote:
Originally Posted by bluebee View Post
Here's a closeup picture of my expansion tank level sensor (more in the threads below):
- Behr radiator and Behr expansion (aka surge) tank autopsy (1) (2) & request for another autopsy (1)
Very good bee and others. I had read this before, but it just did not make it to the "keep" drawer which is my bad. It is ALL coming back to me know. I really think that as I get older, when I add new info into my head, some piece of previously known data gets "pushed out":-(
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Old 05-02-2015, 03:56 PM
Burning2nd Burning2nd is offline
Under the lift arms
Location: Under the lift arms
 
Join Date: Aug 2010
Posts: 5,612
Mein Auto: E39 540, E36 328is, E83x3
Quote:
Originally Posted by TheHockeytowner View Post
Correct me if I'm wrong, but the level sensor does not actually contact the inside of the expansion tank..

bingo...

i freaked out the first time 2...
its magnetic baby!

lol
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