Power steering noise when cold solution

[pollack138]

For a long time I have had an issue with the power steering (asc+t) making a growling/cavitation noise after sitting for more than a few days or so. The noise will go away after running for approximately a minute or two. I found the problem to be the p/s reservoir cap wasn't venting properly and would create a vacuum in the reservoir as the the level dropped due to the bomb being charged after start up. This vacuum causes the cavitation in the pump until air manages to get by the cap's vent. The cap has a slot cut into the surface that contacts the reservoir's top but after time the top became deformed enough (maybe by over tightening the cap?) that the vent no longer lined up properly and caused an air tight seal. I put a split washer between the cap and top as a temporary solution and my noise instantly disappeared. Remove the washer and the growling problem returns. I have tested the system with and without the washer several times over the past few weeks and have had absolutely consistent results - allowing air to enter through the cap/reservoir top area totally stopped the noise.(to test your system just loosen your cap fully and see if noise is gone). I think I will try increasing the length of the cap's vent slot to provide a better solution than using a split washer. Hope this helps some of you that have this annoying problem.

[rosakirk12]

I don't have the problem (yet) but now I know how to solve the problem WHEN it occurs.


Sent from my iPhone using Tapatalk

[8eights]

I have that problem but haven't driven the cars in ages, Great news, Can't wait to try it.

Thanks!

[NevadaMike]

I've been living with that hydraulic pump squeal at startup for 25 years on my '91 850i. It has been sitting for about a month, and today I checked all the fluids and figured, what the heck, and put a split washer over the place where the big top nut meets the lid flange. NO SQUEAL on startup! I can see where the brass inner threaded part has a small slot cut in it, which is obviously there to allow air to enter the reservoir when the pump starts sucking in fluid. It's not doing it's job. My lid and the brass part were both very clean, so it's not because it was gummed up.

Next chance I get I'm going to take that split washer and heat it up to flatten it, and grind a 1/8" slot in it where it's split. I could take a Dremel to that slot in the cover nut to enlarge it, but the price is right for this fix!

Thanks, Pollack138!! Great find!

[tangcla]

Does anyone care to show a photo of what this is?

[pollack138]

Note: this is for an asc+t system. Standard power steering reservoir is different and I don't know if the same situation applies.

cap.png