Hydraulic system fluid flush and renew

[msmith66]

Just so folks can compare, the new fluid looks like canola oil. Mine looked exactly the same and was flushed with ZH-M for $14 a litre.

[lynns]

Originally Posted by msmith66

Just so folks can compare, the new fluid looks like canola oil. Mine looked exactly the same and was flushed with MB-Z for $14 a litre.

Or you can pay $10.25/liter x2+ship at Your Parts Search Returned 2 Part(s) = $29.87

[Gwillie]

Unless I missed earlier discussions, I see no mention of the danger of allowing moisture to get into the system. The hydraulic fluid is hygroscopic meaning that like brake fluid it absorbs moisture from the air. The polyurethane seals although resistant to moisture are not able to last forever and do fail due to exposure to water. Seal experts tell me that a combination of water and heat lead to a rapid kind of seal deterioration that resembles cottage cheese.

A picture of a top lock seal that shows the "cheese" like texture at the failure points is attached.

Others have pointed out in this forum that the original seal material is based on a subgroup of polyesters called polycaprilactones that have improved resistance to moisture and may be the reason for its use.

What all this may mean is that if you don't change your fluid as often as you do your brake fluid (two years?) you will have moisture in your system and probably are cheesing your seals both in the cylinders and in the pump.

You have not found any ph related threats so maybe we should shift attention to the water.

By the way, note that some later model Mercedes reservoirs have a big filter cap that appears to contain silica-gel. Ah ha Mr. Holmes, we may have a clue here.
For those that don't know, silica gel is used to absorb moisture.

Regards,

George Anderson

[Gwillie]

picture of cheese failure. Seal life unknown

[aam]

Hmmmmm.

If fluid circulates then flushing will defenetly help.

But if it only gets pressurized and the pistons go in /out.

Then you can't flush the system much, to make a big difference,
only a small amount from the lines, and pump.
But again, anything is better then nothing.

When you can see pump sediments in the reservoir then replace/ clean.

Now moisture.
Very interesting point George.
I never thought of heat been the cause of seal failure on the front cylinders, but moisture I think you hit the nail on the head.

I personally never had cheese failure seals on my cylinders, only little cracks around the shaft touching area.

Silica in the cap?
George, you are an amazing guy.
Where on earth do you get all that info.
I am very happy to know you.
So if silica is in the cap is there, for one and only one reason,
to absorb humidity..................
You don't want it in the fluid though. LOL.

Regards.
aam.

PS.
Was it Ah ha Mr. Homes?
Or Mr. Robinson.
I say it the same way, but my kids always corect me.
Oh, Hell what do they know.

But my six years old grandson tell me, grandpa you don't
know everything.
Maybe he is right, I am getting confused again. LOL.

[Gwillie]

Thoughts on how flushing works on this hydraulic system. (Based on the service diagrams)

I think the system flushes each cylinder to the reservoir on both strokes of the piston. A short way of saying it is on each stroke, the unpressurized side of the piston is connected directly to the reservoir. By working the cylinders several times, you should change out the fluid if you are catching the return flow in a jug and not letting it back into the reservoir.

George Anderson