W204 C220 air in steering fluid idiocy

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Fridgemagnet

New Member
Joined
Oct 1, 2023
Messages
3
Location
Hampshire, UK
Car
C220
Hi knowledgeable fellow Merc owners - can I call upon your expertise regarding air in the steering fluid? Firstly, I am an idiot - the fluid was air-free before I messed with it. I attempted to introduce some fresh Fuchs CHF 11S steering fluid into the system as the steering can be a little bit whiny and the fluid is black (car is 2011, mileage 130k). I've done this before by sucking fluid out of the reservoir with a syringe, then topping up to the appropriate level with fresh fluid, which went OK the first time I tried it, but didn't make much difference as apparently this needs to be performed several times before the old fluid is sufficiently diluted.

This time I sucked out about 300 ml of old fluid, then topped it up with fresh fluid to the 20 C mark as the engine was cold. That seemed to go well. Then I jacked the front wheels up, and with the engine off turned the steering wheel lock-to-lock a few times. There was some resistance and squelching noises near the lock positions, but otherwise felt OK. I then checked the fluid, and the level in the reservoir had risen greatly and leaked out of the cap a bit, but no signs of froth or bubbles. Next I replaced the reservoir cap and ran the engine (wheels still raised) and listened for signs of pump whining, which sounded fine. I then moved the steering wheel back and forth a little (not lock-to-lock), and it felt horribly notchy, so I immediately turned the engine off. Checking the reservoir, it hadn't leaked again, but the fluid was very frothy. Not good - I think I had sucked too much old fluid out and introduced air into the system.

The question is: what to do next? I won't be driving anywhere with the car in this state, so taking it to a garage isn't really an option. Is it possible for a decent mobile mechanic to bleed the system on my driveway? Most cars seem easily bleedable by the method of disconnecting the return hose, and then pumping the old fluid out with the steering wheel (engine off) while keeping the reservoir topped up, but this method doesn't seem to be recommended for Mercs.

Any help much appreciated! I've only just returned to driving again after shattering a heel bone (not recommended!) and I'm pretty stuffed without a car as I can't walk far at the moment, and can't ride a bike at all.
 
Hello and welcome .

I replaced all of the fluid on mine with a syringe. after each 33 mile drive to work I sucked out as much as I could then topped up with new fluid . took 3 litres of the good stuff before it went bright and clear.

Pretty daft way to replace one litre of pricey fluid but the car was in constant use and I couldnt risk it being out of action . Plus points is no need to get the spanners out and no risk of what happened to you.

I know my story does not help much but someone on here will be along soon with an answer.

Note the reservoir is a throw away service item , the filter for the oil is moulded inside it , available from MB , FCP euro , Autodoc etc .
 
I believe the way to bleed the system is with the engine running and the filler cap removed (put some clean rags on and around it), turn the steering slowly from lock to a few times. It may burp and gurgle a bit but this should remove the air.
 
Thank-you Petrol Pete, Stratman, and alecmascot, I appreciate your knowledgeable advice!

I had another go at it today, and seem to have achieved some sort of success as the steering is no longer notchy and the pump isn't making any horrible noises, although whether the job's a good 'un will have to wait until 5pm when my wife gets home from work to help me by waggling the steering wheel while I check for bubbles. I read the Pelican page before I started yesterday (always a good source of info), and watched some (mostly unhelpful) youtubes. Today I also RTFHM beforehand, and as I was on my own decided to monitor the reservoir with a little USB camera, so armed with the Haynes manual and a laptop I had another go at bleeding. This is what I did:
  1. With the front wheels off the ground and the engine off, Haynes recommend moving the steering wheel lock-to-lock 30 times. For me, that didn't seem to be sufficient, as I was still burping air on and off after about 90 minutes of this. It's also a very messy process as the fluid level rises and falls dramatically, with the occasional small geyser. I wrapped some nice shop towel (i.e., fluff and lint-free) around the reservoir to limit the mess, and changed the towel after each overflow incident, of which there were many.
    After a while I started to improvise, and found that a good technique was to do the lock-to-lock thing a few times to get the fluid (and bubbles) moving through the system, then spun the wheel back and forth quite fast a few times to the extents where it started to meet resistance (but not the end stop at full lock). This would usually generate some satisfying bubbles
  2. Haynes then recommend starting the engine while an assistant has some fresh fluid ready to tip into the reservoir for when the level suddenly drops. I'm on my own today, so I made sure the reservoir was pretty full to start with, then dashed from driver's seat to engine compartment as quickly as my injured foot would allow. I seem to have got away with this, more by luck than judgement - I would definitely recommend an assistant for this step.
  3. Next, Haynes recommend moving the wheel back and forth ±45° a few times with the engine running. Initially this felt horribly notchy, but soon started to feel much smoother, and I started to feel a lot happier.
  4. The final bleeding step is to turn the steering wheel lock-to-lock until bubbles no longer appear, taking care not to linger at the lock positions as big pump strain here. As with all the other steps, it sounds simple, but the Devil is in the detail. After I while, I hit upon the technique of smoothly spinning lock-to-lock a few times, then leaving the steering at dead centre for a few minutes. While resting at dead centre, frothy bubbles would start to appear, and I waited until these had mostly dissipated before repeating the process. Eventually the bubbles got smaller and fewer. I also noted that the steering position close to full lock tended to generate some big bubbles, so I waggled a bit longer in these areas (but not on full lock) until the bubbles stopped... until the steering was in the same position on the next lock-to-lock cycle, when the bubbles would resume again.
Eventually I had to call it a day. I was still seeing bubbles from steering wheel waggling (around dead centre too, not just lock-to-lock), but it's difficult to tell from a camera vibrating from the engine whether these bubbles came from the system or were a product of surface fluid agitation, which is where my wife will (hopefully) help me later on today.

One slightly worrying thing I did notice is that the steering wheel felt very easy to turn shortly after initiating step (4), but got increasingly stiff as the engine got up to full temperature. It might be because the fluid is still horrible and black, or maybe the bleeding process has freed up some crud that is now blocking the filter. I'll keep an eye on that one.

Some pics:

Camera peering into towel-wrapped reservoir:
20231002_105930 Merc steering reservoir and camera.jpg

Laptop on passenger seat:
20231002_110002 Merc steering laptop.jpg

After lock-to-lock on step (4), bubbles would appear after steering wheel was left in dead-centre:
20231002_133350 Merc foamy head.jpg

With hindsight, a splash cover for the camera would have been a good idea:
20231002_142810 camera mess.jpg

The eagle-eyed will have noticed that I've overfilled the reservoir. I did this for the last step as the fluid level rises and falls when the steering wheel is moved, and I didn't want it to drop below the level of the return pipe, which is the mistake I made that introduced air into the system in the first place.

I am leaving the car to cool down now, ready for Mrs Magnet to lend a hand doing a final check for bubbles later. If I'm happy with that, then I'll suck out the excess fluid and go for a test drive. I'll be sure to report back on how this goes.
 
Last edited:
Thank-you Petrol Pete, Stratman, and alecmascot, I appreciate your knowledgeable advice!

I had another go at it today, and seem to have achieved some sort of success as the steering is no longer notchy and the pump isn't making any horrible noises, although whether the job's a good 'un will have to wait until 5pm when my wife gets home from work to help me by waggling the steering wheel while I check for bubbles. I read the Pelican page before I started yesterday (always a good source of info), and watched some (mostly unhelpful) youtubes. Today I also RTFHM beforehand, and as I was on my own decided to monitor the reservoir with a little USB camera, so armed with the Haynes manual and a laptop I had another go at bleeding. This is what I did:
  1. With the front wheels off the ground and the engine off, Haynes recommend moving the steering wheel lock-to-lock 30 times. For me, that didn't seem to be sufficient, as I was still burping air on and off after about 90 minutes of this. It's also a very messy process as the fluid level rises and falls dramatically, with the occasional small geyser. I wrapped some nice shop towel (i.e., fluff and lint-free) around the reservoir to limit the mess, and changed the towel after each overflow incident, of which there were many.
    After a while I started to improvise, and found that a good technique was to do the lock-to-lock thing a few times to get the fluid (and bubbles) moving through the system, then spun the wheel back and forth quite fast a few times to the extents where it started to meet resistance (but not the end stop at full lock). This would usually generate some satisfying bubbles
  2. Haynes then recommend starting the engine while an assistant has some fresh fluid ready to tip into the reservoir for when the level suddenly drops. I'm on my own today, so I made sure the reservoir was pretty full to start with, then dashed from driver's seat to engine compartment as quickly as my injured foot would allow. I seem to have got away with this, more by luck than judgement - I would definitely recommend an assistant for this step.
  3. Next, Haynes recommend moving the wheel back and forth ±45° a few times with the engine running. Initially this felt horribly notchy, but soon started to feel much smoother, and I started to feel a lot happier.
  4. The final bleeding step is to turn the steering wheel lock-to-lock until bubbles no longer appear, taking care not to linger at the lock positions as big pump strain here. As with all the other steps, it sounds simple, but the Devil is in the detail. After I while, I hit upon the technique of smoothly spinning lock-to-lock a few times, then leaving the steering at dead centre for a few minutes. While resting at dead centre, frothy bubbles would start to appear, and I waited until these had mostly dissipated before repeating the process. Eventually the bubbles got smaller and fewer. I also noted that the steering position close to full lock tended to generate some big bubbles, so I waggled a bit longer in these areas (but not on full lock) until the bubbles stopped... until the steering was in the same position on the next lock-to-lock cycle, when the bubbles would resume again.
Eventually I had to call it a day. I was still seeing bubbles from steering wheel waggling (around dead centre too, not just lock-to-lock), but it's difficult to tell from a camera vibrating from the engine whether these bubbles came from the system or were a product of surface fluid agitation, which is where my wife will (hopefully) help me later on today.

One slightly worrying thing I did notice is that the steering wheel felt very easy to turn shortly after initiating step (4), but got increasingly stiff as the engine got up to full temperature. It might be because the fluid is still horrible and black, or maybe the bleeding process has freed up some crud that is now blocking the filter. I'll keep an eye on that one.

Some pics:

Camera peering into towel-wrapped reservoir:
View attachment 147683

Laptop on passenger seat:
View attachment 147684

After lock-to-lock on step (4), bubbles would appear after steering wheel was left in dead-centre:
View attachment 147685

With hindsight, a splash cover for the camera would have been a good idea:
View attachment 147688

The eagle-eyed will have noticed that I've overfilled the reservoir. I did this for the last step as the fluid level rises and falls when the steering wheel is moved, and I didn't want it to drop below the level of the return pipe, which is the mistake I made that introduced air into the system in the first place.

I am leaving the car to cool down now, ready for Mrs Magnet to lend a hand doing a final check for bubbles later. If I'm happy with that, then I'll suck out the excess fluid and go for a test drive. I'll be sure to report back on how this goes.
Hopefully that will sort it !
I did both my cars by this method a few weeks ago.
 
Great write up. Once you get air in there is no easy way to remove it. You have to be patient and keep doing what you did. Well done. Meant to say I think it was the Hello Kitty plaster which made the difference. 😂
 
Jack the front so you can turn the steering easily with the engine off.


Or, for less effort. just drive the car front wheels onto a couple of glossy magazines....same effect.
 

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