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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 03-07-2013, 08:54 PM
panklee panklee is offline
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Mein Auto: 2002 E39 530i,
What is the cause of expansion tank overflow

My 2002 e39 85k miles has been losing coolant for a while now. Once I turned off my engine, coolant started gushing out from the cap. Lost about half of expansion tank. From what I have seen, there doesn't seem to be a crack on the tank.

Would anyone know the cause of this?
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  #2  
Old 03-07-2013, 10:46 PM
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LaCrosse540i6 LaCrosse540i6 is offline
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Were you driving it hard before this happened?

If it wasn't allowed to cool off properly and shut down right away your coolant temp probably rose enough to open up your cap.
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  #3  
Old 03-08-2013, 12:04 AM
edjack edjack is offline
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Two possibilities:

1. You overfilled the tank. When the engine is cold, the top of the float s/b even with the top of the hole.

2. The cap is bad, and cannot hold the pressure.
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  #4  
Old 03-12-2013, 05:44 AM
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540iman 540iman is offline
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+1 over 2 bar pressure or bad cap.
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  #5  
Old 03-12-2013, 06:08 AM
cn90 cn90 is offline
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Either:

1. Bad cap....or

2. Blown head gasket

Did you buy the car recently?
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  #6  
Old 03-12-2013, 04:27 PM
Aussie528iT Aussie528iT is online now
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Normal level in expansion tank when engine is cold is about half full. There is no vent pipe. System vents through cap. Its hollow inside and the outlets are under the 4 "wings" around the edge of the cap.

RonR
99 528iT M52TU
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  #7  
Old 03-12-2013, 09:29 PM
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bluebee bluebee is offline
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Quote:
Originally Posted by Aussie528iT View Post
Its hollow inside and the outlets are under the 4 "wings" around the edge of the cap
Nobody has ever figured out, to my knowledge, how the darn thing works:
- Request for a description of how the expansion tanks works (1)

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  #8  
Old 03-12-2013, 09:44 PM
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bluebee bluebee is offline
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Quote:
Originally Posted by Aussie528iT View Post
There is no vent pipe
My 2002 M54 has an upper overflow hose (see nipple top left in the picture below).

BTW, to get to the bottom of 'how' the expansion tank works, I opened this thread today:
-> E39 (1997 - 2003) > Does anyone have a BMW description of HOW the E39 M54 expansion tank actually works?

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  #9  
Old 03-13-2013, 01:01 AM
Aussie528iT Aussie528iT is online now
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Bluebee,
The nipple on the expansion tank is not an overflow tube. The other end is connected to the radiator via the nipple on the top of the LH/hot radiator tank. The hose goes under the top of the radiator shroud to the nipple on the hot tank. As far as I can work out its a continuous bleed from the hot tank to the expansion tank to remove any air trapped in the top of the radiator. If you take off the cap you will see coolant flow from the hole in the side of the filler neck. What happens when the cap is in place is one of those questions I haven't been able to work out. The hole exits into the neck between the 2 O rings on the cap. I haven't got around to cutting open an old radiator cap to find out. You will notice the top radiator hose has an S shaped section between the bleed nipple and the radiator. This is to stop air trapped in the radiator tank from getting back into the head etc. I have also cut up my old expansion tank to see what is inside. I don't have the level sensor switch (low level instrumet panel and you need the high level panel and the "I" data bus etc) but its a hall effect switch which is triggered by the magnet on the level float.
I think the cover in the other half of the tank is just a stilling arrangment to stop the coolant level sensor from being activated by water flow from the auxiliary water pump. Its operating all the time to ensure enough water is pumped through the heater because of the unusual cooling system flow through the head and block. The M52TU and M54 engines cooling systems are completely different to the earlier single vanos M52 engine whic has a conventional cooling system arrangement. They use a minimal water flow through the block with maximum percisely controlled water flow through the head. At high engine speed and load the aux water pump is needed to ensure adequate flow through the heater as most of the water flow is back to the radiator. There is a PDF on one of the E46 boards which explains how it works but I can't find it right now.
Also don't remove the radiator cap if the engine is hot. Apart from the risk of scalding you can end up with air trapped in the system and then its back to square one and the cold bleed process all over again. How do I know? Been there and done that!
Also don't open any of the bleed screws with the engine hot or cold after you have successfully bled the system. All you will do is let air back into the system. You can test this with the engine cold. Take off the radiator cap and check the coolant level then undo the top radiator hose bleed nipple and observe the water level rise in the expansion tank as air enters the top hose and the water finds its own level in the system. You now have air in the system and have to do the cold rev bleed procedure to bleed the system again. The normal level in the expansion tank is below the water level in the top hose. The water level in the top hose and the engine block, head etc is held there by a sort of syphon effect and opening the bleed screw destroys this and allow air to enter the system.

Hope this helps

RonR
99 528iT M52TU

Last edited by Aussie528iT; 03-13-2013 at 01:10 AM.
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  #10  
Old 03-13-2013, 05:10 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by Aussie528iT View Post
The nipple on the expansion tank is not an overflow tube.
This is interesting, and an excellent discussion. I don't know WHAT it does, but, I too have seen the little hole constantly bleeding coolant INTO the neck of the expansion tank (with the cap removed, and, I think, the aux pump running).

Best place to discuss this is here:
- Does anyone have a BMW description of HOW the E39 M54 expansion tank actually works?
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  #11  
Old 03-13-2013, 04:30 PM
Aussie528iT Aussie528iT is online now
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Bluebee,
There are a number of different threads on the board so maybe they need to be combined. I have read many of them and there are some quite divergent views about the cooling system components and how they work. Many don't understand that the M52 and M52TU engines are completely different animals. It probably would have been better if BMW had called the M52TU the M54 and the M54 the M54TU. The M52TU has much more in common with the M54 than with the M52. The fact that the M52TU has a throttle cable but is still "fly by wire" seems to cause confusion as well.

Regards
RonR
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  #12  
Old 03-13-2013, 05:14 PM
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bluebee bluebee is offline
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Quote:
Originally Posted by Aussie528iT View Post
There are a number of different threads on the board so maybe they need to be combined.
Oh my. I don't know the differences myself.
Personally, I care mostly about the M54 (which is why the one thread I opened was initially explicitly for the M54).

The M54 seems to have the most complex expansion tank; so if we can get a handle on that, the others should be easier to analyze the flow of.

I can rectify the multiple threads by opening separate threads, where we can consolidate the information on the flow through the expansion tank.

Before I attempt that, what SHOULD we open the threads on?
Is this the right set (from the standpoint of the expansion tank flow)?

1. M54 expansion tank fluid flow
2. M52TU expansion tank fluid flow
3. M52 expansion tank fluid flow
4. M62 expansion tank fluid flow

Note: Personally, I'd just do #1 but others may care about the other two.
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Last edited by bluebee; 03-13-2013 at 05:15 PM.
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