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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > DIY Guides > E90 N52 Power Steering Reservoir and Fluid Service DIY (CHF11S)



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      08-18-2019, 12:11 PM   #1
bimmerzeit
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E90 N52 Power Steering Reservoir and Fluid Service DIY (CHF11S)

Have you checked your power steering fluid condition lately? It looks like the previous owner of my 269,XXX mile 328i accidentally filled the reservoir with ATF instead of CHF11S (designated by the green sticker on the fill cap)!

I immediately purchased a new genuine reservoir, as the filter is built into the container itself. New factory clamps, a liter of CHF11S and we are on our way.

Also note, this DIY is specific to E90's *without* active steering. That is a different reservoir. Do also take note some cars may specify ATF. Finally, it is very common for the green CHF11S sticker on your fill cap to fall off over time.

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      08-19-2019, 12:02 AM   #2
porsche959
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Nice vid. Did you drain the entire system before adding the new fluid? Did not see that part in the video...seems like a vital step.
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      08-19-2019, 12:11 PM   #3
bimmerzeit
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Quote:
Originally Posted by porsche959 View Post
Nice vid. Did you drain the entire system before adding the new fluid? Did not see that part in the video...seems like a vital step.
Yeah I drained as much as I could from the reservoir first and then the lines from it. I drove the car for a little while and then sucked out the fluid again, filled with fresh fluid. I plan on doing that a few more times until the fluid stays clean and green.

I'm not sure how one would get 100% of the fluid that remains inside the pump and the rack from a simple drain and fill like I did... maybe a vacuum pump?
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      09-12-2019, 06:46 PM   #4
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Fluid has been sucked out and refilled with fresh CHF11S two more times over the last month and the fluid is finally staying clean and green!
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      10-16-2019, 06:10 PM   #5
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The only PS "flushes" I've come across so far only "suck" fluid from the reservoir. There doesn't seem to be a drain plug system of actually "flushing" clean fluid completely through the lines until you see only clean liquid flowing?

I've seen another flush video where a guy hooks up plastic hose to reservoir return line, jacks up front of car to allow turning of wheels, and uses the steering wheel turn (lock to lock), to pump out the old fluid, while pouring new fluid in reservoir until what's being drained is correct color.

Is something like that possible for the E90?

Last edited by nvargas78; 10-17-2019 at 09:10 AM..
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      10-16-2019, 06:34 PM   #6
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Unless I'm mistaken, ATF is probably the correct fluid for your car. CHF was only specced on cars with active steering (and other gubbins I can't remember right now) running off the PS pump. For cars with only standard PS, ATF is the correct fluid. Filling with CHF on an ATF system won't do any harm, and vice-versa; CHF just maintains correct operating properties under harsher conditions, as far as I know.

Willing to be proven wrong, of course.
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      10-16-2019, 07:00 PM   #7
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Here is a thread on a flush procedure. Unfortunately the pics are messed up

https://www.1addicts.com/forums/showthread.php?t=996184

I've also heard of people undoing one of the reservoir lines and running fluid thru that way.

Also, CHF11 is very common on non-active steering BMW's
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      10-17-2019, 09:17 AM   #8
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Quote:
Originally Posted by gjm120 View Post
Here is a thread on a flush procedure. Unfortunately the pics are messed up

https://www.1addicts.com/forums/showthread.php?t=996184

I've also heard of people undoing one of the reservoir lines and running fluid thru that way.

Also, CHF11 is very common on non-active steering BMW's
Lol...now I know why most PS flushes prefer to only suck from the reservoir... ("1. With the front of the car in the air, remove the front under panel covering the bottom of the engine. I believe I counted 17 bolts total.")

Pretty tempting to just let the PS pump do the work and keep introducing new fluid until the color improves.
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      10-17-2019, 09:59 AM   #9
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Also because step 3 makes a mess, and you should really replace the crush washers if you loosen those banjo bolts. Know from experience!
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      10-17-2019, 01:22 PM   #10
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Quote:
Originally Posted by Tambohamilton View Post
Unless I'm mistaken, ATF is probably the correct fluid for your car. CHF was only specced on cars with active steering (and other gubbins I can't remember right now) running off the PS pump. For cars with only standard PS, ATF is the correct fluid. Filling with CHF on an ATF system won't do any harm, and vice-versa; CHF just maintains correct operating properties under harsher conditions, as far as I know.

Willing to be proven wrong, of course.
The factory fluid reservoir cap on my car had the green CHF11S sticker. It was partially peeling off so I removed it.

That is correct, some cars are ATF others are CHF11S. It does partially depend on options, production date, and apparently there is some random luck to which cars have ATF vs. CHF.
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      10-17-2019, 02:03 PM   #11
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Quote:
Originally Posted by nvargas78 View Post
Lol...now I know why most PS flushes prefer to only suck from the reservoir... ("1. With the front of the car in the air, remove the front under panel covering the bottom of the engine. I believe I counted 17 bolts total.")

Pretty tempting to just let the PS pump do the work and keep introducing new fluid until the color improves.
I've done one just suck and refill awhile back. Sometime soon am going to change the reservoir/filter and probably will do the same maybe 2 empty & refill cycles.

The undershield tray is almost as much fun as the trunk liner.
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      10-19-2019, 03:51 AM   #12
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Quote:
Originally Posted by bimmerzeit View Post
The factory fluid reservoir cap on my car had the green CHF11S sticker. It was partially peeling off so I removed it.

That is correct, some cars are ATF others are CHF11S. It does partially depend on options, production date, and apparently there is some random luck to which cars have ATF vs. CHF.
Random...thanks for that, BMW!
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      10-20-2019, 08:02 AM   #13
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Quote:
Originally Posted by bimmerzeit View Post
The factory fluid reservoir cap on my car had the green CHF11S sticker. It was partially peeling off so I removed it.

That is correct, some cars are ATF others are CHF11S. It does partially depend on options, production date, and apparently there is some random luck to which cars have ATF vs. CHF.
Nope. All E9X are CHF-11S. There is no "random" luck about it; it would be a factory assembly line nightmare to have the same production models assembled "randomly" with different power steering fluid requirements.

It is simply that BMW stupidly relies on the green sticker to remain affixed to the power steering reservoir cap. The cap plastic is embossed with ATF underneath the green sticker because BMW uses the same PS reservoir for models dating back to the 1980's, which do use ATF for the power steering fluid. BMW decided not to produce a distinct PS reservoir cap that was embossed with "CHF-11S Only".

The actual problem is the PS reservoir cap has a thin o-ring that flattens over time and allows fluid to creep past the cap seal. The oil works its way under the green sticker and eventually degrades the adhesive and the sticker falls off. BMW sells a replacement green sticker. Over the past 30 years I've had four BMWs, all which use the same PS reservoir and everyone of them has developed a seal leak at the reservoir cap that is cured by replacing the o-ring.
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      10-20-2019, 08:53 AM   #14
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Not true. My 2007 e91 wants ATF, as verified by BMW when I asked them. If I remember correctly, realoem lists both for my car...
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      10-20-2019, 03:41 PM   #15
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Quote:
Originally Posted by Tambohamilton View Post
Not true. My 2007 e91 wants ATF, as verified by BMW when I asked them. If I remember correctly, realoem lists both for my car...
Well, I guess I should have been specific that I was referring to US-market E9X vehicles. Looking at the TIS parts list, the 325d and 330d (neither sold in the US), use a different PS pump than the gasoline engines, but use the same steering rack as most all E9X (except M3), so based on the different pump used in diesel cars, ATF could be used in the E9X diesel power steering system. It seems the rack can use either oil type.

But there is no way BMW just randomly fills the E9X power steering system with either ATF or CHF-11S. All manufacturers keep very strict configuration management control of the manufacturing process and vehicle part content.
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      10-21-2019, 08:01 AM   #16
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Quote:
Originally Posted by Efthreeoh View Post
Nope. All E9X are CHF-11S. There is no "random" luck about it; it would be a factory assembly line nightmare to have the same production models assembled "randomly" with different power steering fluid requirements.

The actual problem is the PS reservoir cap has a thin o-ring that flattens over time and allows fluid to creep past the cap seal. The oil works its way under the green sticker and eventually degrades the adhesive and the sticker falls off. BMW sells a replacement green sticker. Over the past 30 years I've had four BMWs, all which use the same PS reservoir and everyone of them has developed a seal leak at the reservoir cap that is cured by replacing the o-ring.
There is a ventilation hole in the cap, a safety overflow valve that dumps excessive vapors or even fluid out of the system aka to your engine bay... no o-ring will fix this...
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Last edited by streetpro; 10-21-2019 at 08:38 AM.. Reason: added picture
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      12-07-2019, 06:54 AM   #17
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Quote:
Originally Posted by streetpro View Post
There is a ventilation hole in the cap, a safety overflow valve that dumps excessive vapors or even fluid out of the system aka to your engine bay... no o-ring will fix this...
Streetpro, can you provide info on the reservoir you used to capture overflow from PS Cap? Thanks!
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      12-08-2019, 12:37 AM   #18
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Put the wrong fluid in and you may have to replace the PS pump. Previous owner of my car had to. $700+ for the part.
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      12-09-2019, 03:08 AM   #19
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Originally Posted by BruceJ View Post
Streetpro, can you provide info on the reservoir you used to capture overflow from PS Cap? Thanks!
Any generic motorcycle brake fluid reservoir from AliExpress will do... I had to drill a hole in the cap as it was getting pressurized...
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      12-15-2019, 06:39 AM   #20
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Quote:
Originally Posted by streetpro View Post
Any generic motorcycle brake fluid reservoir from AliExpress will do... I had to drill a hole in the cap as it was getting pressurized...
Then how do you keep the pressurized fluid/vapors from escaping the hole drilled in the cap of the motorcycle brake fluid reservoir...?
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      12-16-2019, 01:43 AM   #21
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And why would I want to have it pressurized, there is no point in that... either you allow the gasses/fluid to go via this route or they fight their way around the lid as they have done before...
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      09-14-2020, 07:10 PM   #22
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I miss this car. My neighbor bought it a year ago and its still going strong, nearing 300,000 miles!!
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