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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 06-30-2014, 04:39 AM
danlau danlau is offline
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Mein Auto: 1995 BMW 525i
Power steering reservoir

Hi, I have a 2003 BMW 525i, and I notice that there is a small leak of power steering fluid. It seems to come from the ventilation hole on the cap of the reservoir. I wonder if I need a new reservoir. I am a new DIYer, and need some advice.

Thanks in advance!
DanLau
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  #2  
Old 06-30-2014, 07:32 AM
jygesq jygesq is online now
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it is normal

some people put end of Q tip in the vent hole.
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  #3  
Old 06-30-2014, 08:00 AM
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cdawg246 cdawg246 is online now
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Change out the o ring on the cap first its cheap and that may be your problem


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  #4  
Old 06-30-2014, 08:04 AM
pleiades pleiades is offline
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Quote:
Originally Posted by danlau View Post
Hi, I have a 2003 BMW 525i, and I notice that there is a small leak of power steering fluid. It seems to come from the ventilation hole on the cap of the reservoir. I wonder if I need a new reservoir. I am a new DIYer, and need some advice.

Thanks in advance!
DanLau
The O-ring in the cap might be bad, but also check to see that you have the level correct. The dipstick has a max mark that's only about 1 cm up from the tip. Don't overfill.

.... Also .. ... if you look at the cap, it should have an "ATF only" mark on top. Don't put anything else in there.

Last edited by pleiades; 06-30-2014 at 08:07 AM.
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  #5  
Old 06-30-2014, 11:48 AM
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540 M-Sport 540 M-Sport is online now
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Venting is NORMAL for the cap, and the residue that accumulates on the reservoir is normal/common. While I have not seen much residue on other cars I have with similar ZF reservoirs, it is my opinion, there is a particular trait that is causing this...could be higher operating pressure, or whatever. All I know is I keep the level correct, no higher than maximum. I have replaced the entire reservoir, as well as the cap, and o-ring...even the "upgraded" larger/fatter o-ring someone came up with and sent to me...still leaks/vents. I'm over it and will just keep cleaning the outside off it each time I change the oil.

BTW, I have not tried the Q-tip trick, only because I don't wish to obstruct or cause a pressure build up from doing so. While the risk seems very low...It just isn't that big a deal to mess with any further.
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Last edited by 540 M-Sport; 06-30-2014 at 06:38 PM.
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  #6  
Old 06-30-2014, 12:04 PM
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bluebee bluebee is offline
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Type /power steering reservoir f3 in the bestlinks and this pops up, among others:
- What to do if your power steering reservoir cap is always wet (1)

See also:
- What to do if your power steering reservoir cap is always wet (1) & how to clean the power steering fluid reservoir internal filter (1) (2) & what is the generic size of the power steering reservoir cap o-ring (1) & what is the most often recommended power steering fluid (1) (2) what volume do you need to buy & (1) how to do a power steering fluid flush DIY (1) (2) (3) (4) & how to replace the cap o-ring (1) (2) & why you want to fix the power steering hose drip onto the alternator (1) (2) (3) & how to debug PSP power steering pump noises (1) (2) (3) or steering rack noises (1) & a nice power steering pump autopsy photo (1) & how to flush cloudy ATF fluid (1) (2) (3) (4) (5) & what PS fluid to use (1) (2-pdf) (3-volume) & DIYs to replace the power steering hoses (1) (2) (3) (4) (5) & how to debug common BMW power steering issues (1) and noises (1) (2) (3) or steering rack noises (1) & does an ATF leak from power steering hoses onto the alternator really cause the bearings to fail (1)
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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
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  #7  
Old 06-30-2014, 12:36 PM
crazy4trains crazy4trains is online now
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Just cover the reservoir with an old ankle length sock. Use the sock to wipe the reservoir when you remove it to check the fluid level. Replace the sock over the reservoir when done. This will keep everything in the vicinity clean.

The reservoir is designed to vent. DO NOT block the vent!!!
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  #8  
Old 06-30-2014, 07:31 PM
danlau danlau is offline
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Thank you all very much for all the information. I will try to replace the o-ring first. I will also read all the links that bluebee provides and decide what to do next if replacing the o-ring doesn't work.
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  #9  
Old 07-01-2014, 07:05 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by crazy4trains View Post
Just cover the reservoir with an old ankle length sock.
If you're gonna do it properly, it must be a BMW-badged sock!
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See also: E39 Bestlinks & How to easily find what you need
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  #10  
Old 07-01-2014, 03:30 PM
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Quote:
Originally Posted by danlau View Post
Thank you all very much for all the information. I will try to replace the o-ring first. I will also read all the links that bluebee provides and decide what to do next if replacing the o-ring doesn't work.
My advise is to do nothing. It vents, it is normal...live with it. Don't OCD over it.
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  #11  
Old 07-01-2014, 04:29 PM
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chiefwej chiefwej is offline
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I thought it was the vent, but changing the O ring made the "leak" go away, at least for a couple years. Time for another new O ring.
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  #12  
Old 07-02-2014, 08:59 AM
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bluebee bluebee is offline
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Quote:
Originally Posted by chiefwej View Post
I thought it was the vent, but changing the O ring made the "leak" go away, at least for a couple years. Time for another new O ring.
As far as I can tell, if we replaced the o-ring, and then never opened the thing ever again, it wouldn't ever mist the outside of the cap.

At least that was my experience.

Of course, we have to open the thing, just to check, so, as a pragmatic matter, it requires a new o-ring every couple of years.

Best to buy your o-rings en masse, along with the other spare parts:
- What is the generic size of the power steering reservoir cap o-ring (1)

See also:
- Glovebox printouts for emergency use (1) and how to save $ money to qualify for free shipping on UPS/DHL/USPS/FedEx by stocking O-rings & gaskets & bulbs & vacuum hoses & fuses & wiper blade inserts & belts & bearings & oil filters & cabin air filters & engine air filters & fluids in your garage whenever ordering from the recommended parts suppliers.
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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
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  #13  
Old 07-02-2014, 10:25 AM
small_525 small_525 is offline
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540 M-sport I'm sorry the 2.5 didn't do the trick for you? I've been meaning to add to that original thread that I started with regard to size and how its working. Since I didn't use the car much during the winter I don't have many miles on it yet to say who well it works. While its been less then 4000 miles since it was installed its worked "so far" at keeping the top of the canister clean ! I seem to be leaking from the hoses now There have been a few people that I've sent the o-rings to I wonder how the others are doing? I never put any "filter" in the vent hole but blew compressed air through so it was clean. I'm thinking that any restriction allows it to build more pressure and causes issues. Like putting your thumb over a garden hose. I don't think I'm leaking at the hoses now that its been blown clean. Again too few miles to say for sure.

I've still got a fist full of the 2.5mm rings if anyone is looking.
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  #14  
Old 07-06-2014, 03:03 PM
danlau danlau is offline
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I have replaced the o-ring and there seems to be no leaking any more.

Thank you all for your help!
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