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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 03-12-2013, 09:43 PM
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bluebee bluebee is offline
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Does anyone have a BMW description of HOW the E39 M54 expansion tank actually works?

EDIT: As per filon102 below, we should strive to locate a good BMW description, with fluid flow diagrams, of how the expansion tank works for all three major E39 engines (M52, M54, & M62).

A recent thread got me thinking again, after about a year or two since I had autopsied my 2002 expansion tank, whether anyone actually knows HOW the thing works.
> E39 (1997 - 2003) > What is the cause of expansion tank overflow

The first chamber is simple enough - but the second chamber seems classically diabolical, in how it works, and what the flow is through the expansion tank via the six separate openings in the M54 expansion tank (I think the earlier E39s had less complicated expansion tanks, and I think the E46 M54 expansion tank is also a bit different):
  • Top
    • Filler cap (2 bar venting)
    • Filler neck (aux pump inlet hole?)
    • Overflow hose nipple (connects to the upper radiator nipple)
    • Bleeder screw (one of two bleeder screws on the M54, the other being in the upper radiator hose near the thermostat)
  • Bottom
    • Hose 1
    • Hose 2
    • Electrical connector to the "low coolant" sensor
The question posed in this thread is:
Q: Does anyone have a BMW description of HOW the E39 M54 expansion tank actually works?

See also:
- 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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Last edited by bluebee; 03-28-2013 at 04:53 PM.
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  #2  
Old 03-12-2013, 10:17 PM
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bluebee bluebee is offline
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Here is a diagram of the flow through the M52 (simpler) expansion tank:
- M52_technical_information.pdf (977.8 KB, 663 views)
- BMW_M52TU_engine_training_manual.pdf (978.0 KB, 166 views)

We need the same type of diagram for the M54 & the M62 showing the flow through the expansion tank:
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Last edited by bluebee; 03-12-2013 at 10:41 PM.
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  #3  
Old 03-12-2013, 10:30 PM
filon102 filon102 is offline
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it would be nice if you could also expanded it to the m62 engines too...

but i believe its just any regular expansion tank... its got a floater in there to tell you when your low on coolant. I dont think its that complicated bee
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  #4  
Old 03-12-2013, 10:57 PM
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bluebee bluebee is offline
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Quote:
Originally Posted by filon102 View Post
it would be nice if you could also expanded it to the m62 engines too...
It makes sense that we should UNDERSTAND the flow through all three major engines of the E39 family.

I don't have anything from BMW other than these documents (we need better):
Quote:
Originally Posted by filon102 View Post
but i believe its just any regular expansion tank... its got a floater in there to tell you when your low on coolant. I dont think its that complicated bee
I disagree. You're only talking about the EASY stuff. That's only half my expansion tank.
I believe the upper aux pump inlet and the upper overflow and the two sliders and two chambers, one of which has two openings at the bottom, all make the M54 operation much more than just what you've intimated above.

It may end up to be simple, but, still ... nobody, to my knowledge, has explained how the flow works through the M54 expansion tank (which has five fluid openings to deal with!).

For example, what do you think the purpose of the second chamber black slider is?
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Last edited by bluebee; 03-13-2013 at 06:43 PM. Reason: Added M54 expansion tank pictures.
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  #5  
Old 03-13-2013, 05:16 AM
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bluebee bluebee is offline
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This interesting description was on the other thread:

Quote:
Originally Posted by Aussie528iT View Post
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 instrument 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 arrangement 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 which has a conventional cooling system arrangement.

They use a minimal water flow through the block with maximum precisely 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 siphon effect and opening the bleed screw destroys this and allow air to enter the system.
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Last edited by bluebee; 03-13-2013 at 06:44 PM.
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  #6  
Old 03-13-2013, 05:31 AM
JimLev JimLev is offline
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Quote:
Originally Posted by filon102 View Post
it would be nice if you could also expanded it to the m62 engines too...

but i believe its just any regular expansion tank... its got a floater in there to tell you when your low on coolant. I dont think its that complicated bee
I should be able to get my hands on an expansion tank from an '00 M62tu engine soon.
I was changing a friends lower oil pan gasket last night and he mentioned that his temp gauge was creeping up and he would experience a loss of heat. I looked in the expansion tank and the stick was ~2" above the top of the tank.
However, looking into the tank showed that the coolant level in most of the tank was at the bottom and the level where the stick is was high. Almost like the stick side and the rest of the tank was isolated.
We filled the tank to 1/2 full and he will drive it and see if the temp and heat are normal.
When he gets the new tank we'll cut this one open.
This car has 175K on it, the cooling system, with the exception of the clutch fan, is original....no need to post about him needing to replace the cooling system.
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  #7  
Old 03-13-2013, 05:32 PM
Aussie528iT Aussie528iT is offline
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Bluebee,
A bit more info.
The flow into and out of the expansion tank goes something like this:

1/. Water flows from the level sensor side to the aux water pump. This is the lower of the 2 hoses that run along the bottom of the radiator.
2/. It is then pumped into the area at the rear of the main water pump via the plastic pipe that enters the rear area of the main water pump.
3/. It then passes through the block/head and flows out via the coolant pipe that runs under the inlet manifold. This is the hot water supply to the heater valves mounted on the LHS of the engine bay on the strut tower. This occurs with the engine running or not. If the engine is off the "REST" heating function has to have the aux pump running. (Since you have an M54 I think this is controlled by the "MAX" button)
4/. It then passes through the heater valves to the twin heater cores and returns to the expansion tank via the upper hose at the base of the radiator and enters the other side of the expansion tank.
5/. The flow at the nipple at the top of the tank is always into the tank from the radiator hot tank but is it continuous or just when the expansion tank cap is off? I don't know. It depends on how the cap is constructed internally.

The aux water pump has 3 functions:
1/. To provide water flow through the heater when the "REST" function is used.
2/. To provide adequate water flow through the heater when you are doing 200+kmhr down the autobahn.
3/. To assist the cold bleed process to ensure water is pumped through the engine and heater core to help flush out any air. The "cold rev" part of the bleed process is also to help bleed air out of the heater cores. It uses the main water pump while the thermostat is still closed to force all water flow (apart from the small bleed from the radiator hot tank) through the heater core.

Its worth noting that for other than max or min heat, the heater valves pulse open and closed for between 0.3 and 3.3 secs depending on what temperature is set on the heater control panel. If the setting is at minimum heat the valves are closed continuously. If the setting is max heat the valves are open continuously. (You can see this if you have the INPA diagnostic programme)
With the ignition off the heater valves are normally open unless you stop and do a quick shop visit. In this situation the valves close for a period to prevent getting a hot air blast from the heater when you start the engine. (heat soak effect)
The pulsing action of the valves is presumably to prevent the valves sticking either open or closed but that's just speculation on my part.

The thermostat is in the cold water return from the radiator and controls the cold water temp INTO the engine not the more conventional water temp OUT of the engine. On the M52TU and M54 engines the thermostat is fully open at 97degC. If you go to test 7.0 after unlocking the instrument panel you can watch the temp change as the load on the engine changes and the engine DME varies the MAP controlled thermostat opening. The DME activates the heater in the thermostat to fool it into thinking the water from the radiator is hotter than it actually is so that it is fully open at a lower temp than 97degC

OOPS! I think I got a bit off topic here. Its all useful info though.

Hope this helps
RonR

Last edited by Aussie528iT; 03-13-2013 at 07:04 PM. Reason: Added thermostat info and spelling corrections
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  #8  
Old 03-27-2013, 01:25 PM
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bluebee bluebee is offline
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For the crosslinked record, JimLev kindly posted an expansion tank autopsy here:
> E39 (1997 - 2003) > 540 Expansion Tank issue. Bluebee U were looking for this info

Quote:
Originally Posted by JimLev View Post
I posted this same info over on Roadfly, unless you have an account there you can't view the pics.

540 Expansion tank problem and dissection

A few weeks ago I helped a friend change his lower oil pan gasket on his 2000 540ia.
He mentioned that when driving on the highway and then needing to slow down because of traffic the heat would sometimes go cold and the temp gauge would start to rise. Throwing the car into neutral and giving it gas would bring the temp gauge back down and the heat would return.
After the oil pan gasket job was done I took the cap off the expansion tank. Looking inside the level didn't look right.
The left side of the tank was almost empty, it should be 1/2 full. This is the section that fills the waterpump/engine.
The section of the tank that the stick is in was full to the top part that the stick traverses thru. Didn't look right to me.
We dumped more coolant in even though the stick showed it was overfilled.
He ordered a new expansion tank. The previous tank was installed in '08 and was not an OEM BMW tank.
Last Sat. we installed the new tank and all is well.
We then cut the tank open to find out what the problem was. This tank seems way more complicated than it needs to be...must be the German way of doing things?
There are 4 sections inside the tank which should all be connected to each other thru openings in the lower wall partitions.
3 of them were connected, but the important section wasn't.
If you purchase a non-BMW tank pour a little water into the tank before you install it. It should run out the bottom hose connection that goes to the waterpump.
Anyone ever run into this problem before?

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Quote:
Originally Posted by bluebee View Post
Thanks JimLev, for the expansion tank autopsy, and, for the picture of the passageway that was never cut out at the factory.
This information can be helpful for this thread:
- Does anyone have a BMW description of HOW the E39 M54 expansion tank actually works?

So that this information is found easily in the future, I will cross reference this thread to the existing expansion tank autopsy threads - so that we can get a better handle on how the thing works.
- Behr radiator and Behr expansion (aka surge) tank autopsy (1) (2) & request for another autopsy to understand the function of that second (black) chamber & pinned float (1)

It would be nice if someone can explain with an exploded picture HOW the expansion tanks works (at least the flow of fluid, with arrows going in and out).

I, for one, still don't understand at all how the "black" section works!
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  #9  
Old 03-28-2013, 04:47 PM
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bluebee bluebee is offline
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For the record, JimLev posted a nice picture of the operation of the 540 expansion tank today:
> E39 (1997 - 2003) > 540 Expansion Tank issue. Bluebee U were looking for this info

I'm not sure if the M54 is the same though ...
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  #10  
Old 03-28-2013, 08:08 PM
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bluebee bluebee is offline
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Below is an M54 composite cooling system from the following diagrams:
What would be nice is if we can together, draw the flow diagram.
Here are all the parts.

If someone can help with the fluid flow diagram, I can clean it up.
All you need to do is print this, scribble on it, snap a photo, and I will clean it up.
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Name:	bmw_m54_cooling_system_flow_diagram.jpg
Views:	991
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ID:	368704  
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Last edited by bluebee; 03-28-2013 at 08:46 PM. Reason: Working on the diagram
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  #11  
Old 03-29-2013, 09:47 AM
YinD YinD is offline
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cleaned up image

wanting to help... so I cleaned up the image that bluebee had. Not a I6 owner so I cant do much more that this.
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