What causes power steering fluid to turn dark?

[KevinMalone]

~25k miles ago, I flushed the power steering fluid in our 2004 Volvo V70 with CHF 11S where I disconnected the return line and cycled fluid through the system until the fluid was new. The CHF 11S started lightish green but is now more or less brown. There doesn't seem to be anything ferrous in the fluid when I tested it with a neodymium magnet. For comparison, I did a drain and fill on our 2009 BMW E90 with CHF 11S 25k miles ago, and the current fluid is still light green.

An internet search suggests that the power steering hoses are deteriorating? Would it be beneficial to add a Magnefine filter on the return line?

 

[dishdude]

The seals/hoses are breaking down. Everything in the system is 20 years old.

 

[Boomer]

You are seeing carbon (used in making rubber products) being released from the degrading rubber lines. Best to replace the lines at this point. However, I don't think the fine carbon particles will hurt anything. But if larger pieces of rubber are being released into the fluid, then you could generate pump problems.

 

[97K15004WD]

A filter will work fine on that as long as you keep changing it frequently at first. I used a WIX 33033 for my power steering fluid filtering and it worked very well.

Start here:

M

Post in thread 'Need to install a power steering filter in Chrysler minivan'

Jan 9, 2022

Wix 33033 is 3/8 metal can, 15 microns I believe,

Wix 33032 is 5/16
Wix 33031 is 1/4

I put mine on the return line to the reservoi…

• mattwithcats

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[SHOZ]

I had that bad on a used Taurus. Started out like black coffee. I flushed it and it came right back as the new fluid cleaned up things more. Ended up do weekly, then a couple of monthly flushes with cheap ATX fluid until it stayed clean with the drop on a napkin test.

 

[Dave9]

I wouldn't bother. Either change the hoses, or don't.

 

[JRay’07]

Another possibility is that your Volvo places more stress on the fluid which causes it to oxidize and break down faster. The only way to verify this would be to monitor the temperatures and pressures within both systems and compare the results.