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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 06-12-2012, 06:29 AM
Qbrozen Qbrozen is offline
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sticking coolant float?

So I just did a full cooling overhaul. The problem I'm having is that the float does not rise back up when the car cools down.

So I open the cap and look... float is at or near the bottom. I can tap it and it will rise back up. Put cap back on, drive to work, leave car for day. Get back in to start it up and it tells me coolant is low. Turn off car, open cap, repeat procedure.

Anyone else had this problem? Is there anything I can do? Or is the new expansion tank defective?
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  #2  
Old 06-12-2012, 07:53 AM
pleiades pleiades is offline
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On a new tank with dry internals, it's not unusual for this to happen *initially* but if it's repeating itself, yeah could be defective. Once the floater is floating, it shouldn't drop *unless* you had a large air bubble that allowed the exp tank level to fall.

What brand tank did you install?

Be absolutely sure you've done the bleed procedure right and eliminated all air pockets, otherwise more serious problems could show up.
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  #3  
Old 06-12-2012, 08:46 AM
Qbrozen Qbrozen is offline
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I thought about the air pocket. I've done 2 different bleed procedures (initially when I filled, where I ran the car with heater on and bleed screw open, then again just yesterday where I followed the directions about starting cold, heater on, and revved it several times with bleeder screw open and cap loosened). The temp gauge has been rock solid from the getgo ... an air pocket usually causes this to fluctuate, no?

i installed the uro tank.
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  #4  
Old 06-12-2012, 09:01 AM
pleiades pleiades is offline
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Quote:
Originally Posted by Qbrozen View Post
i installed the uro tank.
This is probably the culprit. Uro is the least-trusted, lowest-quality brand in the BMW universe.

Go to the dealer and get a genuine tank.
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  #5  
Old 06-12-2012, 09:38 AM
Qbrozen Qbrozen is offline
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I know. I just figured for that ONE part, how bad could they screw it up. I have seen a number of posts with people using the Uro expansion tank, so kinda took a leap of faith on that one. I actually had to look it up when you asked to make sure that was what I ordered. I do know I didn't trust Uro for the new fan blade. That was too big a risk.

Still... I'm just going to have to see if I can figure out a way to make it float more freely before taking the damned thing apart again.
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  #6  
Old 06-12-2012, 09:44 AM
pleiades pleiades is offline
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Quote:
Originally Posted by Qbrozen View Post
I know. I just figured for that ONE part, how bad could they screw it up. I have seen a number of posts with people using the Uro expansion tank, so kinda took a leap of faith on that one. I actually had to look it up when you asked to make sure that was what I ordered. I do know I didn't trust Uro for the new fan blade. That was too big a risk.

Still... I'm just going to have to see if I can figure out a way to make it float more freely before taking the damned thing apart again.
Check out this post-mortem...

http://www.bimmerfest.com/forums/sho....php?p=6115130

BTW, get the tank from a BMW dealer. Even the aftermarket Behrs are unreliable. I bought a Behr from an online vendor and had to return it because the seam between the top and bottom parts was cracked. I got the genuine from my local dealer and turns out the price was virtually the same as the one I returned to the online vendor.

Last edited by pleiades; 06-12-2012 at 09:47 AM.
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  #7  
Old 06-12-2012, 09:49 AM
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Fudman Fudman is offline
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Quote:
Originally Posted by Qbrozen View Post
I just figured for that ONE part, how bad could they screw it up.
The answer is pretty bad. The expansion tank is one of the several items (like FSU) that REQUIRE an OEM dealer sourced replacement. Replace the expansion tank and your problems will disappear.
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  #8  
Old 06-12-2012, 11:22 AM
Qbrozen Qbrozen is offline
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*sigh*
alright. thanks, guys. On the bright side, I still have some BMW coolant left over.

I will say, I inspected the tank and it seemed to be pretty nice. Looking at that thread linked above, it definitely looked like the dealer unit on the left as opposed to the chinese unit on the right. I guess its not so nice on the inside.
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  #9  
Old 06-12-2012, 11:59 AM
pleiades pleiades is offline
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Quote:
Originally Posted by Qbrozen View Post
*sigh*
alright. thanks, guys. On the bright side, I still have some BMW coolant left over.

I will say, I inspected the tank and it seemed to be pretty nice. Looking at that thread linked above, it definitely looked like the dealer unit on the left as opposed to the chinese unit on the right. I guess its not so nice on the inside.
Maybe the floater is just catching on a piece of plastic "burr" left over from the molding process. However, the floater shouldn't be dropping back down if the coolant level is stable and your system is air-bubble free.
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  #10  
Old 06-12-2012, 03:34 PM
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530iman 530iman is offline
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Uro exp tank

The float is catching on left over burr or material as the previous poster said, I have a uro tank and it does the exact same thing, its been good to me for about a year know and 12,000 miles no leak or problems. I bought the Uro because it was readily available around the corner but I planned to replace it with OEM to match the rest of my cooling overhaul but have not seen a need. After removing the cap you have to tap the float stick slightly, no need to worry unless you see white residue on or near the tank
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  #11  
Old 06-12-2012, 03:44 PM
Mikes530 Mikes530 is offline
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I still have the original OE tank and my float has been doing as you described since the day it had 0 mi on the clock. Never a problem, I just tap the float stem and it pops up.
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  #12  
Old 06-13-2012, 07:13 AM
Qbrozen Qbrozen is offline
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Originally Posted by Mikes530 View Post
I still have the original OE tank and my float has been doing as you described since the day it had 0 mi on the clock. Never a problem, I just tap the float stem and it pops up.
Huh. Now that is interesting. So does your coolant level warning come on, too?

Playing with it this morning, I am kind of suspecting it is sinking with pressure in the system. I'm not an engineer, so this is total guessing on my part. But the float doesn't actually POP back up. It slowly rises. When I unscrew the cap, even after sitting for a couple of days, I get the woosh of decompression. The float will then actually start to slowly move. So my theory (today ) is that the float is defective and the higher pressure overwhelms it. When the pressure is relieved, it can rise back up.

Does that make any sense?
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  #13  
Old 06-13-2012, 07:14 PM
Mikes530 Mikes530 is offline
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Quote:
Originally Posted by Qbrozen View Post
Huh. Now that is interesting. So does your coolant level warning come on, too?
Never had a warning light. I don't get any pressure woosh or any other noise when I remove the cap.
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  #14  
Old 06-14-2012, 06:14 AM
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Fudman Fudman is offline
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Quote:
Originally Posted by Qbrozen View Post
Huh. Now that is interesting. So does your coolant level warning come on, too?

Playing with it this morning, I am kind of suspecting it is sinking with pressure in the system. I'm not an engineer, so this is total guessing on my part. But the float doesn't actually POP back up. It slowly rises. When I unscrew the cap, even after sitting for a couple of days, I get the woosh of decompression. The float will then actually start to slowly move. So my theory (today ) is that the float is defective and the higher pressure overwhelms it. When the pressure is relieved, it can rise back up.

Does that make any sense?
Not really. The float rises and falls with coolant level and not with internal pressure within the expansion tank. It floats on the coolant due to lower density. Pressure has nothing to do with it.

When the engine heats up, coolant expands and increases pressure in the cooling system. This causes coolant to flow into the expansion tank and that level to rise. The empty space above the coolant in the expansion tank allows for this expansion. The internal pressure in the expansion tank is related to the volume of empty space. As the coolant level in the expansion tank rises, the volume of empty space decreases. This causes the air to compress and the internal pressure to rise. If it exceeds the cap (rated at 2 bar) pressure, it will vent. Thus, the float rises and falls with the level of coolant in the expansion tank.

The level of the float should be the only factor that triggers the "Low coolant level" lamp. If you have insufficient coolant, it will not rise high enough while driving and will trigger the warning in the hot condition. What is confusing is that your float is below the coolant level during the cool down period. This should not occur as the coolant level rises when hot and lowers when cold. Your coolant level may be low or you may need to bleed air from your system.

Alternative expansion tanks have a documented history of premature failure (do a search). While yours could last 4 year or 4 weeks, I would recommend replacing it with a dealer sourced (or a Behr with the BMW label ground off) tank and keep the Uro as a spare.
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  #15  
Old 06-14-2012, 06:35 AM
Qbrozen Qbrozen is offline
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Originally Posted by Fudman View Post
Not really. The float rises and falls with coolant level and not with internal pressure within the expansion tank. It floats on the coolant due to lower density. Pressure has nothing to do with it.

When the engine heats up, coolant expands and increases pressure in the cooling system. This causes coolant to flow into the expansion tank and that level to rise. The empty space above the coolant in the expansion tank allows for this expansion. The internal pressure in the expansion tank is related to the volume of empty space. As the coolant level in the expansion tank rises, the volume of empty space decreases. This causes the air to compress and the internal pressure to rise. If it exceeds the cap (rated at 2 bar) pressure, it will vent. Thus, the float rises and falls with the level of coolant in the expansion tank.

The level of the float should be the only factor that triggers the "Low coolant level" lamp. If you have insufficient coolant, it will not rise high enough while driving and will trigger the warning in the hot condition. What is confusing is that your float is below the coolant level during the cool down period. This should not occur as the coolant level rises when hot and lowers when cold. Your coolant level may be low or you may need to bleed air from your system.

Alternative expansion tanks have a documented history of premature failure (do a search). While yours could last 4 year or 4 weeks, I would recommend replacing it with a dealer sourced (or a Behr with the BMW label ground off) tank and keep the Uro as a spare.
So what is happening then, I presume, is that the level is rising, but of course since the top of our float rods are held in place by the cap, the float is forcefully submerged in the rising coolant. The car cools and the coolant recedes, but the float stays submerged and sinks with the coolant level. I figured maybe the pressure wasn't allowing it to rise back up. Again, just a guess, but based on the fact that, when I remove the cap and relieve the pressure, it will slowly rise. Either way, it is apparently a defective float.

I plan on selling the car soon, so I'll have to replace it as suggested. Thanks for all the replies.
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  #16  
Old 01-04-2013, 07:22 PM
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gtxragtop gtxragtop is offline
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I replaced mine about 18 months ago when I did the cooling system overhaul. It is a Behr unit but not from dealer stock. I'm constantly getting low coolant warnings typically after 5-7 miles of driving starting from a cold engine. Each time I look, enough antifreeze but the float is no longer working well. Almost like the float material has become water logged and now poorly floats. Never had this issue with the 6 year old OEM tank.
Bah, cheap parts.

PS: All was fine until 6 months ago when the warnings were very intermittent. Now, they are every day.
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Last edited by gtxragtop; 01-04-2013 at 07:23 PM.
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  #17  
Old 01-04-2013, 07:58 PM
mbell666 mbell666 is offline
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Behr tanks are bad, I recommend you swap it out for BMW one asap. I had two fail on my car both lasted ~8 months, quite few other people had same issue on here.
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  #18  
Old 01-05-2013, 06:20 AM
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mpower997 mpower997 is offline
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What about meyle Expansion tanks? Autohausaz.com has behr listed as OEM

Last edited by mpower997; 01-05-2013 at 06:22 AM.
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  #19  
Old 01-05-2013, 07:19 AM
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Fudman Fudman is offline
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The only reliable source for a replacement expansion tank is the dealer. Any other brand, to include Behr, bought anywhere else has a documented history of premature failure. This is not to say a third party expansion tank WILL fail prematurely nor will a dealer-sourced expansion guarantee reliable operation. The widespread anecdotal evidence indicates that the probability for premature failure of a third party expansion tank is noticeably higher than a dealer-sourced expansion tank. Hence, you roll the dice when buying any brand tank from any source other than the dealer.
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Old 01-05-2013, 08:56 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by Fudman View Post
The only reliable source for a replacement expansion tank is the dealer. Any other brand, to include Behr, bought anywhere else has a documented history of premature failure. This is not to say a third party expansion tank WILL fail prematurely nor will a dealer-sourced expansion guarantee reliable operation. The widespread anecdotal evidence indicates that the probability for premature failure of a third party expansion tank is noticeably higher than a dealer-sourced expansion tank. Hence, you roll the dice when buying any brand tank from any source other than the dealer.
I'm gonna add that quote to:
- What BMW E39 parts & supplies are best to buy OEM (1)

Unfortunately, my 1.5-year old expansion tank is leaking ...

EDIT:
The OP will benefit from these autopsy photos:
- Behr radiator and Behr expansion (aka surge) tank autopsy (1) (2) & request for another autopsy (1)
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See also: E39 Bestlinks & How to easily find what you need

Last edited by bluebee; 01-05-2013 at 08:59 AM.
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