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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 09-08-2012, 12:44 PM
usedbimmer usedbimmer is offline
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Mein Auto: 1997 540i
Expansion Tank leaking coolant on top. Can this be fixed?

My Radiator, Expansion Tank, water pump and thermostat have all been replaced in the last 11 months. Last night had a puddle of fluid under my car - and I've found out it's coming from my new expansion tank!


The fluid appears to be leaking out of the top. Adjusting the mounting screw on top appears to make it worse until I opened up the cap and released the pressure. I'm pretty sure I've got a crack, but not certain. Does the screw possibly have anything to do with the leak? How far can / should I tighten it?

See pic:
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Last edited by usedbimmer; 09-08-2012 at 12:46 PM.
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  #2  
Old 09-08-2012, 01:04 PM
anton831 anton831 is offline
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Mein Auto: 528i
Partscontainer on ebay selles them cheap I will be buying one also soon
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  #3  
Old 09-08-2012, 01:21 PM
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Fudman Fudman is offline
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Is your expansion tank a Behr? Is it an OEM or delaer purchased? If not, you've probably bought an aftermarket or Chinese-made Behr. All of these commonly fail prematurely. Get the right part from the right source and you can forget about premature failures. Or try and save a few dollars and roll the dice...
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Old 09-08-2012, 01:22 PM
usedbimmer usedbimmer is offline
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I'm not nearly so worried anymore after looking at this DIY. Looks like a quick simple fix, though may be a little messy with coolant leaking.
This is one of the few things I think I can do myself. Thanks.

http://www.bimmerboard.com/forums/posts/46816
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  #5  
Old 09-08-2012, 01:24 PM
usedbimmer usedbimmer is offline
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Hi, Fudman:

My Replacement tank is a Behr - and the certified master mechanic at my local repair shop ripped me off to the tune of about $189 for it.
Perhaps, not having the thermostat and water pump replaced right away played a role in having it bust so prematurely?
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  #6  
Old 09-08-2012, 03:11 PM
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Topaz540i Topaz540i is offline
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That screw is used for bleeding air out of the system. It should have an o-ring on it. Many companies sell it in brass because it is known to break.
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  #7  
Old 09-08-2012, 04:00 PM
usedbimmer usedbimmer is offline
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Topaz: hmmm.. When I loosen the screw, the coolant leak got worse? Is it possible it just wasn't tight enough? So far, I'm not seeing a crack, but it's hard to tell unless I remove it and take a good look.
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  #8  
Old 09-08-2012, 04:14 PM
edjack edjack is offline
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The screw does not have to be terribly tight tho seal; some break it by tightening.

Did you replace the cap with the tank? It may not be holding pressure.
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  #9  
Old 09-08-2012, 04:15 PM
mbell666 mbell666 is offline
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Replace the tank with BMW one. For 100 bucks it not worth the stress or risk to the engine.

Opening the screw allows air in and coolant out of the tank.
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  #10  
Old 09-08-2012, 05:15 PM
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Topaz540i Topaz540i is offline
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i never had the screw problem. I have only seen others report it. Like edjack said it doesnt need to be super tight. It has an o-ring. Check that the o-ring isnt damaged.

I didnt have a cap leak but i def had a cap wear out for some reason.

http://forums.bimmerforums.com/forum....php?t=1777214
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a.f.e. c.a.i.
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ss braided brake lines

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  #11  
Old 09-08-2012, 09:59 PM
usedbimmer usedbimmer is offline
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Tightening or loosening the screw when the engine is hot seemed to increase the flow of coolant leaking out. I don't think the screw is damaged - and the cap is certainly holding the pressure in. I think the thing is cracked somewhere up on top.
It's not worth the hassle - I'm going to replace it with a cheap, $45 unit and get rid of this car once and for all. I'm going to lease something new and not have to worry about car repairs anymore.
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Old 09-08-2012, 10:21 PM
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bluebee bluebee is offline
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This is the canonical thread on the bleeder screws:
- Brass bleeder screws (1) (2)

And this one on the new expansion tanks:
- Why new made-in-China Behr/Hella expansion tanks are DOA (1)

Lot's of good DIY information here:
- Removal instructions for the alternator & drive belt system of a 2002 525i
- Removal instructions for the fan shroud of a 2002 525i
- Tools necessary for a cooling system overhaul
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Please read the suggested threads, where the best 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; 09-08-2012 at 10:22 PM.
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