Hydraulc fluid on E320 W210

[rallen]

Does anyone know what it is for? Is it for the steering wheel pump?

It is below the minimum currently and would like to know what to use to top it up / change it. The service book does not refer to it at all, so I presume one never changes it. But on older cars I have noticed it becomes thin, watery like, so I am sure it does need to be changed.

"Hydraulic fluid" is typically the name used for brake fluid > as the brakes use a hydraulic piston/cylinder design.

MB use DOT-4 fluid. [at least my 97 C230 uses DOT-4]

Brake fluid should be changed every two years > as it is "hydroscopic" >> it absorbs water vapor > which in turn lowers the boiling point of the fluid > which lowers the thermal efficiency of the fluid.

There is a specific "power steering fluid" for the power steering system of the car

[jcyuhn]

Is this a station wagon or sedan - they are different.

The wagon has a reservoir in the front, left corner of the engine compartment. That reservoir feeds an engine driven hydraulic pump. The pump supplies both the power steering and the self-leveling rear suspension.

The sedan has a more conventional setup, with an engine driven power steering pump with integral reservoir.

I'm not up to speed on the fluid requirements for either...

- JimY

[rallen]

Yes it is the "wagon" (we call them estates here).

The service booklet does not mention it, but I know on my old Peugeot the steering pump fluid was getting hot (that is normal) and very very watery, so I changed it. So do I need to change it at all? The car is 4 years old and has covered 25K miles.

[TROVERMAN]

On my 95 e320 wagon (124) it has the pump which operates the rear self-leveling system and the power steering. However, the power steering fluid resevoir is located directly atop the pump, while the rear leveling suspension resevoir is located in the left front corner of the underhood area, and uses a special fluid which I purchased from MB. My car was low on this fluid for some time however, with seemingly no side effects.

[jcyuhn]

Ah, I neglected to notice you were across the pond, otherwise I would have directed you to examine beneath the passenger side of the bonnet...

The 124 and 210 chassis estate cars are rather different in this area. The 124 uses a "dual pump" which provides hydraulic pressure for both power steering and self leveling, but uses separate fluids to do so. It contains a typical small reservoir for the power steering fluid and in addition is plumbed to the larger reservoir for the leveling system. A common problem is a failing seal and the pump mixing the two fluids together.

The 210 is simpler, with only the larger reservoir and the same hydraulic fluid powering both steering and suspension.

MB does not specify any change interval for this fluid (neither did they for the 124 suspension). The conventional wisdom on the earlier cars was to change the fluid every 3-4 years. My personal opinion is don't bother, that is overkill. With only 25K miles in four years, just top off the fluid and don't worry about it. Your owners manual should specify the fluid required. Likely it is only available at the main dealer, or from a Mercedes specialist.

- JimY