Does anyone have a BMW description of HOW the E39 M54 expansion tank actually works?

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:

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 :dunno:

This interesting description was on the other thread:

Aussie528iT said:

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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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

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

JimLev said:

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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bluebee said:

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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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 ...

Below is an M54 composite cooling system from the following diagrams:

• E39 => 525i => 11 Engine => 11 35 Engine Cooling => COOLING SYSTEM-FAN/FAN COUPLING
• E39 => 525i => 11 Engine => 11 35 Engine Cooling => COOLING SYSTEM WATER HOSES
• E39 => 525i => 11 Engine => 11 35 Engine Cooling => WATERPUMP - THERMOSTAT
• E39 => 525i => 17 RADIATOR => 17 05 Radiator => RADIATOR/EXPANSION TANK/FRAME
• E39 => 525i => 17 RADIATOR => 17 05 Radiator => TRANSMISSION OIL COOLING
  
• E39 => 525i => 64 Heater and Air Conditioning => 64 18 WATER PUMP, VALVE, HOSES => HOSES F PUMP AND VALVE/AUTOM.AIR COND. <== Automatic AC
• E39 => 525i => 64 Heater and Air Conditioning => 64 18 WATER PUMP, VALVE, HOSES => WATER VALVE/WATER HOSE
• E39 => 525i => 64 Heater and Air Conditioning => 64 15 HEATER RADIATOR => HEATER RADIATOR AUTOMATIC AIR CONDITION <== Automatic AC
• E39 => 525i => 64 Heater and Air Conditioning => 64 15 HEATER RADIATOR => HEATER RADIATOR AIR CONDITIONING
  

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.

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.

There is a very good attempt at explaining how the flow works through the expansion tank made over here today ...
> E39 (1997 - 2003) > Will the next person who replaces his expansion tank please cut it open & compare?

I'm hoping that OP will come here to expand upon what we need to know!

Speedex750 said:

• I've cut open a failed tank, there's a complex arrangement of chambers, tubes and connected chambers comparable to Bluebee's E39. There are three main chambers all open to the filler neck at the top, one for the bobber, one for the level alarm float and a third for the heater hose connection. In addition there's a connection from the top hose terminating in a small hole into the top neck just under the filler cap. Chambers are interconnected by holes in the bottom, all flush with the bottom of the tank. It appears that filling an empty system would be through the hose connection on the bottom and side to the heater, air bleeding back through the engine via the top hose until it runs from the bleed screw. Final air bubbles come back pushed by the coolant pump through the small bleed hole dropping the tank level slightly. You can see this happening by running the engine without the cap on. Revving the engine up shows how big the flows are, there's a big overflowing swirl.
• The E85/86 level bobber is separate to the level indicator float that works in the same way as the E39 with an annular magnet triggering a reed switch in an encircled dry pocket. A new switch still brought up the light; the original switch was found to work OK with an external magnet. Playing around with the cut open tank showed that in the approximately 1" of total float travel; in the bottom part the switch stayed open circuit, in the middle the switch goes closed circuit and then just at the top of the float travel it goes open circuit again which will put the warning light on. I believe the magnet may not be as powerful as the original and lets the switch open when the coolant level is OK. Or alternatively the float and magnet can move further up than in the original tank. I'm working on extending the reed switch about ¼" further up to keep it closed circuit when the float is at the top of its travel. There can't be much coolant left by the time the warning light comes on.

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This post is interesting in terms of how the system works.
> E39 (1997 - 2003) > E39 suspected pressure in the cooling system

dvdlkd said:

Martin,
I'll assume your 97 523 cooling system is similar to my 97 528. Let's assume your car has been bled correctly, and the expansion tank is at the correct level when cold (full kalt mark on the expansion tank). If you open the expansion tank, you should not see a level change or hear any hiss. However, if you then go open a bleeder screw, you will get a hiss as air is sucked back into the system. This is because your system (radiator, expansion tank, upper part of engine) is equalizing coolant level with the expansion tank. If vented properly, the system is water solid everywhere except the expansion tank. The upper part of the engine and radiator are water solid and at a higher level than the level at full Kalt in the expansion tank. You now need to go through the vent procedure again. With the expansion tank and both bleeders open:
1) Fill coolant/water mix into expansion tank until a solid flow comes out the lower bleeder on the thermostat housing. Then replace this bleeder.
2)Fill coolant/water into the expansion tank until you get solid water out of the expansion tank bleeder. This gets the upper radiator water solid. You will notice that the expansion tank is almost overflowing to get the upper radiator water solid. After being patient with this and getting to water solid out of this bleeder screw, install the bleeder screw.
3) Now, and this part is important, draw down the level in your expansion tank to the full Kalt level so you don't over pressurize the system when you run the engine. Install the expansion tank cap.

I left out turning the heater on at full hot temperature, but from your post, you know to do that through this procedure.
Now run the car till it gets to full temperature. You may still have some air in the upper engine. If you have no other problems or leaks with your cooling system, this air will make it to the radiator and expansion tank via the vent hose that runs along the top of the radiator to the expansion tank. When the car cools down, you may need to add a little more coolant to get back to full kalt level. But if your system is not leaking, you should have to add coolant but once or twice and it should stay at full kalt when cold.

I would not be pulling bleeder screws unless you are doing some cooling system maintenance. You will need to run the bleed procedure if you do.
Hope this helps. I understand the elevation issue but don't know if I described clearly enough above.

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