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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

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 08-24-2012, 09:48 PM
rdl rdl is online now
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Leaking Bleed Screw

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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  #2  
Old 08-24-2012, 09:53 PM
cn90 cn90 is offline
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Maybe time to switch to brass screws, about $4-5 at autohausaz or rmeuropean.
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  #3  
Old 08-24-2012, 10:30 PM
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bluebee bluebee is offline
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Quote:
Originally Posted by cn90 View Post
Maybe time to switch to brass screws, about $4-5 at autohausaz or rmeuropean.
This thread is good backup for the official brass screw thread:
- How to retrofit brass bleeder screws (1) (2)
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Each repair should invariably add to our knowledge base by the process of inexorable incrementalism.
Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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  #4  
Old 08-25-2012, 06:53 AM
rdl rdl is online now
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Originally Posted by cn90 View Post
Maybe time to switch to brass screws, about $4-5 at autohausaz or rmeuropean.
I had seen the brass bleeder screw threads & thought they were overkill. The plastic screw seemed perfectly adequate so long on one didn't overtorque and twist the head off or otherwise damage it physically. I've always been careful & thought I had nothing to worry about. It never ocurred to me that the plastic screw could fail in the way mine did.

But brass now looks pretty good, especially since the plastic one was $7.56 at the dealer here in Ontario.

I thank my lucky stars that this happened around home, close to the dealer and not on trip a few hundred miles out the back of beyond.
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  #5  
Old 08-25-2012, 07:09 AM
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Topaz540i Topaz540i is offline
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i just ordered a brass screw from pelican for $4.25 it was actually cheaper than the plastic one lol
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  #6  
Old 08-25-2012, 07:13 AM
cn90 cn90 is offline
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The plastic screw: it is kind of hollow in the core, plus people sometimes over-tighten it.
The brass screw is much better.


Many years ago, when BMW used aluminum tstat housing (I used to have a 1983 735i),, everything from the tstat housing to the bleed screw was aluminum, so it was not an issue at all.
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  #7  
Old 08-25-2012, 09:46 AM
rdl rdl is online now
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Out of curiosity, I cut the screw in half with a Dremel. I still can't find any trace of the crack that is leaking, although the cutting action could easily have folded plastic over the crack path.

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It is a real puzzle to me how this screw could crack and leak given the shape. It's not as though the configuration is a hollow shell. The hole down the centreline is small diameter and barely extends into the threaded barrel.

All the more reason to go to brass I guess.
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Old 08-25-2012, 10:03 AM
Jim Rolando Jim Rolando is offline
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The bleeder screw on my expansion tank is brass. But, the one on the top hose connection failed exactly as you describe and I replaced it. Next time I replace it it will also be with a brass one.
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  #9  
Old 08-26-2012, 03:09 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by rdl View Post
Out of curiosity, I cut the screw in half with a Dremel
Nice.

I wish we would ALL autopsy our failed parts (I'll bet 90% of the knowledge of what fails would be found that way!).

I'll add it to the autopsy photos!
- Behr radiator and Behr/Heat expansion tank autopsy (1) (2) & request for another Behr surge tank autopsy (1) & why new Behr/Hella expansion tanks are DOA (1)
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Each repair should invariably add to our knowledge base by the process of inexorable incrementalism.
Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need

Last edited by bluebee; 08-26-2012 at 03:11 AM.
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