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Flushing the Power Steering
Hydraulic System
By Paul Waterloo

If you have an A8 (additional notes for a C5 A6 at the bottom of the procedure) that is at least five years old or plan to keep it for a while, it's a good idea to replace the power steering hydraulic fluid. The good news: it's relatively easy. Do it every 60,000-75,000 miles and the pump and rack have a chance of lasting longer.

Tools and Materials Required Procedure
Remove the hydraulic reservoir by lifting it out of its cradle. The supply line comes from the transmission cooler in the radiator, it is the lower, smaller hose. The return line to the pump is the higher, larger line.

Wipe down the reservoir. Remove the factory clamp on the return line by prying it with some needle nose pliers. Place a bucket under the reservoir, take off line and drain reservoir into bucket.

Drain reservoir after removing lower, supply line.

Remove the filter from the reservoir. Clean it to remove any foreign material. I used brake cleaner over the bucket that I used to drain the fluid into. I then sprayed it with compressed air to clean and dry it.

Flushing the System
One the reservoir is empty and the filter cleaned, place a golf tee in the supply line of the reservoir. This will allow you to fill the reservoir with fresh fluid and not have it leak out.

Fill the reservoir with fresh hydraulic fluid. It will take the entire liter of fluid. Place the supply line into the empty container and ensure it won't tip over.

IMPORTANT: Do not run the car for more than 4 seconds in the following step so that the reservoir will not go dry.

Start the engine and count 4 seconds. Turn off the engine. This pumps clean fluid from the reservoir to the pump, through the system. The old fluid is collected in the empty container. 4 seconds of engine operation will pump about 2/3 liter through the system.

Empty the collection bottle. Place supply line back in it.

Fill the reservoir again. Start the engine and run for 4 seconds. Secure engine. If you pour some of the fluid out of the collection bottle, you will see that it is clean. This completes the flush.

NOTE: If you run the car more than 4 seconds each time, you could consume more than 2 liters of fluid. If this happens and the second run through the system produced clean fluid in the collection bottle, use it to top off the system.

When complete, install the supply line with a new hose clamp, replace the return line with a hose clamp if you'd like. If it's leaking, please do.

Place the reservoir back into the cradle and top the fluid just below "full" because the fluid is ambient temperature and will expand as it heats up to normal operating temperature.

Notes on Doing a C5 A6 from Jon Cole:
On the '01 A6 you have to unbolt the reservoir from the side of the engine compartment, no big deal at all. The bottom of the reservoir rests in a padded press fitting, you have to lift it out firmly but gently.

The supply side line seems much shorter than on the A8, too short to get up and into an empty bottle, so I put a piece of extension hose on it (not sure of size, I use it for my shop vac and coolant (but it's clean). One advantage was that the clear extension hose looped up high enough before going into the bottle that I could see what was pumping into it, both as to amount and color.

You also have to remove a plastic housing that holds about 5-6 electrical connectors, I moved it up out of the way and held it there with a velcro strap around it to support it, and reinstalled it.

The reservoir on the A6 holds less than the A8, apparently; refilling the reservoir uses maybe 1/3 to less than 1/2 liter. So I cranked for only 1-2 seconds at a time rather than 4 - that emptied the reservoir.

Upon refilling I let it bleed some air out (you could see slow bubbling and a tap or 3 with a screwdriver helped it along) before doing the next pump sequence. Did about 4 2 second pumps and that pumped about 1.5 liters, at which point it was running nice & green. A 1" hose clamp will work on the supply line but a smaller one fits better.

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