Greetings Audi vets and fellow enthusiasts!

First off, I thank anyone and everyone in advance for ANY assist you could lend regarding this issue... I sincerely apologize if I've missed a sticky or overlooked a thread in my search...

I bought a 2006 Audi A4 2.0T Quattro (red) with 201k miles and a known GROSS PS leak. Evidence of RED synthetic fluid was leaking fairly rapidly, and after troubleshooting, it became clear that I needed to replace the Rack and pinion assembly. I purchased a slightly used OEM rack (listing suggested that it only had 66k coming from an 08 A4), but it did have some residual RED (presumably synthetic) PS fluid within. After some tinkering and a little learning curve, my dad and I managed to get the new used rack installed complete with NEW OEM Banjo bolts and crush washers.

Research led us to purchasing GREEN CHF 11S mineral oil fluid. All information pointed to the CHF 11S being compatible with CHF 202 (I believe). We understood that mixing the residual RED synthetic with GREEN mineral could have adverse effects, but we pressed on. We flushed the PS system to the best of our ability to where the color was predominantly green and seemed to give us a good starting point. In checking for further leaks, the gross leaks were resolved with the rack swap and we have been unable to reproduce any other leaks, except... when we drive the car for roughly an hour around town, the PS (presumably the pump) begins to groan and moan with very little steering in either direction. In addition, we are keeping a close eye on the PS reservoir and are seeing consistent foaming within the reservoir and at times causing overflow of the fluid onto the exterior body of the reservoir. We see this especially the longer we drive the car (I'm guessing as the car and system gets hotter?).

Would VERY much welcome your thoughts, advice and experience with the PS foaming issue.

Given the lack of parts that make up the PS system, we are wondering if the issue is one of the following or perhaps a combination of:
a) the mixing of the 2 unlike fluids (synthetic & mineral)?
b) air getting into the system somehow?
c) the PS pump beginning to fail?
d) clamps on the reservoir and pump hoses causing a small leak or air to get into system?
e) overlooked issue with rack or banjo bolts/crush washers?
f) noobs who have NO idea what they're doing??? (likely this answer)

Thank you kindly in advance,
DluA (James)

 

Found this thread in another forum
https://www.audiworld.com/forums/a4-...ystem-2796052/

Turns out, there is a L-shaped screen filter that should be seated in the bottom of the return side (low pressure) of the power steering reservoir.

Mine was dislodged, causing the bubbling and geyser like action in my reservoir while running and getting worse the more you drove it.

Either replace reservoir making sure screen is seated or tinker with existing screen and seat (takes some playing with).

Best of luck! My power steering is working beautiful now!