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Old 08-26-2012, 04:12 AM
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bluebee bluebee is offline
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Location: San Jose, California
 
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K
RDL posted an autopsy photo of his bleed screw, which failed up the middle!
-> E39 (1997 - 2003) > Leaking Bleed Screw
Quote:
Originally Posted by rdl View Post
I've seen posts mentioning broken and leaking bleed screws, but had always assumed that the heads had broken &/or leaked around the O-ring under the screw's head. I'm posting my experience so that others may check before replacing an expansion tank.

I popped the hood this morning to check oil level and found the dreaded white anti-freeze spatter around the expansion tank. There was also liquid coolant on the top ledge/seam of the tank. The bleed screw was dry with no visible defect. I was sure I had a cracked tank.

To make a long story short, I found the fault was the bleed screw leaking through the centre; not past the O-ring seal and not the tank. But, liquid would bubble up from the bottom of the large X in the screw head when the engine was running and up to normal temp, i.e. pressure. The screw has a crack through the centre although for the life of me I can't find it, even with a jeweler's loupe and a dental pick under a bright light.

Anyway, I replaced the screw for a few dollars & no more leak after a 30 minute drive.

The red arrow indicates the leak. The blue arrow points to the seam with standing liquid. There was liquid around the entire perimeter of the tank. You can also see some of the white spatter deposits on the engine and tank.
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