visal911

Hello everyone,

I recently bought an 05 E55 that seemed to have a small power steering leak. The pump was whining, fluid was bubbly, i could hear the pump cavitating and fluid was leaking out of the reservoir cap. With the cap open and the engine on the fluid was FOAMING. I thought there was air in the system.

I replaced the reservoir and the reservoir seal with OEM parts, bled the system with wheels up in the air till the bubbles stopped coming out. After the process was done, everything seemed fine. The power steering pump was perfectly quiet with no whining or groaning at all. Which makes me think my pump is still good. I checked the fluid level and filled it up to the proper level at 80C.

After another drive a couple of hours later I started to hear the dreaded PS pump whine and look under the hood and see power steering fluid has leaked out of the cap again. Any ideas on what it could be?

Thanks in advance.

visal911

Before:



After

bbirdwell

I had situation like this once. Turned out to be a bad bearing in the power steering pump that was heating up and literally causing the hydraulic fluid to boil. Put an IR thermometer on the pump and/or fluid and check the temperatures.

Alternatively, pressure valve is stuck and the fluid is again heating up from being churned by the pump because the fluid is not circulating through the steering rack. Less likely scenario since you wrote that could bleed the system.

visal911

Thanks bbirdwell!

I'll check the temperature and report back. The pump running super smooth and quiet after the initial bleeding procedure makes me believe the pump is still ok. I'll bleed it again and see what happens.

visal911

Well,

Seems like I definitely have air getting into the system instead of an boiling issue. Bled the system again, went for a drive - car and pump was quiet and smooth. Parked up for the night and it started FOAMING out of the cap again on a cold start and the pump started whining a couple of seconds later.

Will be visiting my mechanic to check for leaks. Hoping it's the pump or a line instead of the rack, area around the rack does seem pretty dry.

new55

What PS fluid do these things use ? I think I may try to refresh mine - is there an easy way to drain , I was going to use a turkey baster and extract as much as I can then refill? Thx

visal911

They use CHF 11s fluid.

https://www.fcpeuro.com/Mercedes~Ben...&t=5&b=5&d=&v=

SICAMG

Could very well be the pump internally cavitating. Just put one in my car...real easy job.

StarvingArtist

Isn't CHF 11s green? or maybe blue can't remember. That looks brownish yellow.

visal911

I believe it turns brown after a couple of years of use.

visal911

UPDATE.



Took the old pump out and it had about half a inch of play in the shaft. Put in a new pump with the new reservoir and the PS system is fixed!

bbirdwell

Glad to see you got it repaired and I'm glad that my diagnosis was correct.

May you have many more happy miles of driving!

wfooshee

Like I said, they very probably saw "pressure low" codes and assumed it was the pump, not the accumulators.