How to Change Mercedes W123 Power Steering Fluid and Filter

Written By: Nicolas Siemsen

Comments: 17

How to Change Mercedes W123 Power Steering Fluid and Filter

Difficulty

Easy

Steps

Time Required

30 minutes

Introduction

The most often neglected fluid and filter on the W123 cars is the power steering fluid and power steering filter.

Learn to change yours today, and extend the life of your pump and steering gear box.

Tools

Parts

Mercedes-Benz Approved Power Steering Fluid

Step 1

Jack up the front of the car so you can turn the steering wheel while the car is stationary.
See the guide on jacking up your car, if you need guidance on this.

Step 2

To start the process of changing your power steering fluid, you'll need to remove the lid on the pump reservoir.
If you want guidance on this, and on checking the fluid level, see the guide on checking power steering fluid level.

Step 3

With the lid removed you can see that this fluid is a bit low, and is also very dark/dirty.

Step 4

Remove the nut holding down the spring and plastic retainer, if present. On some cars, there is just a spring as shown in the second picture which should be removed.
The nut on this car is a 10mm.

Step 5

Now use your fluid extractor, or turkey baster (never use it in the kitchen again!) to remove enough fluid to get easy access to the filter.
Dispose of the fluid in your drain pan.

Step 6

Remove the filter using a pair of needle nose pliers.

Step 7

See how nasty this is? This may be the original filter, almost 30 years old...
Nice fresh filter picture, ready for install.

Step 8

With the filter out, you can remove the remainder of the fluid in the reservoir.

Step 9

Install your new filter. Install it with the holes facing upwards, as shown.

Step 10

Replace the spring, retainer and nut over the filter and tighten down. The spring should still have some room to expand and contract but should be snug.
Fill the reservoir to the bottom of the metal rim around the top of the pump housing.
This car is getting power steering fluid, instead of automatic transmission fluid. Both are OK. The power steering fluid is clear.
Now, turn on the engine. Be sure the car is in park or neutral first. Turn the steering wheel left and right, as far as it will go, a few times to get out any air.
Top off the fluid as needed. Never let the pump run dry.
If your fluid is very dirty, simply repeat the process of sucking out fluid, putting the filter back in, filling the reservoir, and then running the engine and turning the wheel until it looks clean.

Great job keep up the good work!

cbelle1 - 15/07/17

Hallo, ich bräuchte die MB Teilenummer für die Deckeldichtung. Hat die hier jemand? :)

Max VOGEL - 07/05/22

You really want to flush the fluid properly. Disconnect the return hose to the reservoir and have a friend run the engine. Collect the fluid now pumping out of the hose whilst you top up with clean fluid. When the hose runs out of dirty fluid and you see the colour of the new fluid, cut the engine. Top up to the correct level and the flush is complete.

Chiswick Classics -

Conclusion

Finish by re-installing the cap and taking it for a test drive.

Author

Nicolas Siemsen

Member since: 07/12/13

39532 Reputation

14 comments

I find this tutorial so simple to follow. I prefer images and text to video. Well done!!!

Holden Belmont - 21/08/16

Holden, I am glad it was helpful! I agree, I usually prefer good pictures and text to a video - no need to rewind when you miss something.

Nicolas Siemsen - 22/08/16

Agreed. Very well done !

susan vernon - 20/11/16

Thank you so much for your detailed guides! What sort of symptoms could we expect if the power steering fluid or filter need replacing?

Angel Jon Camama - 24/11/16

This was so professional; technical writers take notice!

Brian Graham - 30/11/16

Good job plain and simple thank you

Mike - 03/01/17

Question: Why do I need to jack up the car? Can't I just turn the wheels with the tires on the ground?

David Ballard - 28/03/17

You could. However, turning the wheels while the car is on the ground and not moving puts substantial strain on the pump. If the front wheels are hanging freely in the air that is not an issue. Your pump, your car, your choice :) I would jack it up.

Nicolas Siemsen - 29/03/17

Beautifully explained and illustrated.

Thank You for helping our old cars on the road.

Terry Harris

thar1914 - 21/08/18

How often should you ideally replace the fluid and filter? I’m guessing every other year…

Paul Alexander - 10/12/20

On my old mustang I leave the low pressure hose off into a bottle and run the engine for a couple of seconds to drain the old PS oil in the system. New oil in the PS a pump reservoir, obviously. Can this be done on the ‘85 300D? I don’t see this hack on any of the forums? Thanks

albert scalla -

How much oil do you need for a full change? Thank you

Ghita Andrei -

Too bad this great ifixit is wrong. Just like any other W123/300D fluid change there is a proper DRAIN PLUG at the lowest point on this system on the bottom of the steering box! Put your drain pan under the steering box by the knuckle and the drain plug is right next to it. Remove the plug and it drains the whole system, lines, steering box and all...not just the reservoir. Replace the plug after you swap out filters and the whole system will have fresh MERCEDES steering fluid. Plug in and retightened refill then start diesel and swing from lock to lock to bleed.

Larry Butler -

Thankyou so much !

You should have been a teacher 😜

Maybe you are you ,never the less ,Thankyou 🙏

I have a 1978 W123 250 straight 6 and wondering if the process is the same as what you have just explained with your model ?

Drayon Lowe - 27/02/24