In this write-up I'll be explaining the process on how I like to flush power steering fluid. (Also chilton's way) I performed it on my 2002 Pontiac Grand Prix. This should be performed, in my opinion, as often as you change your transmission fluid; but GM does not specify an interval. Most people do this when their pump starts making noise, but I'm doing it as preventative maintenance. Besides, my old fluid had a burnt smell to it. My pump was completely silent before, and still is after the flush. It's not hard to do, but since our reservoirs are in an unthinkable place (behind the engine on the passenger side for those who do not know) you may want to be under the car. You may be able to do everything from above, but you have to get under to put a pan down, and the process is easier with the wheels off the ground anyway, so that's how I'll be explaining the procedure. If done correctly, no air will be introduced to the system during this process.
This process if very efficient since never will any old fluid that goes through the rack, go back into the reservoir. The order of fluid would be: Reservoir, pump, rack, and back to the reservoir. I remove the return line that goes back to the reservoir so it will not cycle. I've seen a method of removing fluid from the reservoir and replacing with new, starting, and repeating. The problem with that is the reservoir accounts for about 1/4 of the system capacity. So the first flush would change 1/4 of the fluid, then the next is already partially new fluid, and so on. Never would you be able to flush that system out completely, there will always be a percentage of old fluid left that would keep getting smaller eventually but never completely. It is good to flush completely to remove particles or sediment in the system that will wear the components. There is no filter in the power steering system.
Being that this is a return line, there is no pressure. It is actually often referred to as the suction line.
Things you will need:
2-3 quarts of new power steering fluid (Use power steering fluid with stop leak additives if your system leaks. Most 100K+ systems leak into the rack boots and you may not know it), Jack+Jack Stands, 10 mm Socket+Ratchet, Pliers, "3/8'' dummy hose"(To keep fluid from coming out of the reservoir. A bag and rubber band may work too), Drip pan, long funnel, a medium sized container to monitor the flushed fluid's color, towels.
Things that will help:
Fluid siphon pump(some way to get old fluid out of the reservoir), Flashlight, gloves, cardboard to put down before starting, 3/8ths line to extend the return line into a container
Raise and support the car with jack stands. Put a tarp/cardboard under the car if you don't want to make a mess. Remove the coolant overflow tank and set it aside for easier access to the power steering reservoir (10mm). Remove the power steering cap and remove the old fluid. You can do this with a vacuum bleeder tool, a hand siphon pump, or even a turkey baster. If you really don't have any of these, you may remove the return line and the fluid will dump out. I suggest going with the other methods over this because it will drip all over the frame and cv shaft.
Once the old fluid is removed, remove the return line from the reservoir, and direct it into a container. Some fluid will come out. I used some old transmission cooler line to extend it by inserting it into the return hose. Then make sure fluid will not come out of the reservoir where you removed the return hose. I used some transmission cooler hose with a bolt in the other end.
You can see the reservoir at the other end of the hose with a bolt in it. If you don't have 3/8'ths hose, find some way to plug that inlet hole. A bag and rubber band may work too. You can also see the return line being redirected with a steel line. If you don't have a line like this, find some way to direct the hose into a pan or bucket. Fluid will come out of it fairly quickly. Position a pan or bucket under the return line.
Now you can fill the reservoir with new fluid using a long funnel. Fill it until it's nearly to the top.
Now you will be starting the car for short amounts of time. Take note that the reservoir empties quickly. It only takes about 3 seconds from the time you start cranking to completely drain it.
Since the wheels are in the air, you will be able to do this process quickly. Start the car for just 2 seconds, then shut it off. Refill the reservoir completely. Check the color of the fluid in the flushing container, and dump it into another container so you can monitor the current fluid color.
My first flush:
Start the car again for two seconds, and shut it off. Fill the reservoir, and check the fluid condition. It should start becoming clear by the second time. I could see the fluid coming out of the return line very slowly was clearer than the fluid in the container, so the new fluid had already made it through.
Now that the new fluid has made it through, you will turn the wheel while starting for the 2 second period.
Start the car for 2 seconds, during that time, turn the wheel completely to one direction, and shut it off when you get there. This should be a very quick process. You can start turning the wheel while it's cranking.
Here is a quick video I made of this process to help describe the duration: Flushing Power Steering Fluid - YouTube
Fill the reservoir. You will see that the flushed fluid is now dark again. Turning the wheels displaces more old fluid in the rack. Keep starting and turning lock to lock quickly until the fluid in the container becomes close to the new fluid color.
My 3rd time flushing while turning the wheel: It's getting lighter.
My 4th time flushing while turning the wheel(6 total flushes): This is light enough. My new Valvoline fluid is a very light yellow color. At the time I flushed this, the fluid slowly dripping out of the return line was a little clearer than the fluid in the container. (Unmixed with the dirtier fluid) This is after a total of flushing twice without turning the wheel to start, and 4 times while turning it. I used 2 quarts during this process, and it was already clean enough for me.
Once you're comfortable with the fluid color, do not add any more fluid to the reservoir because you will have to remove the dummy hose from the reservoir and fluid will come out. Install the reservoir cap(to create a slight vacuum so the remaining fluid in the reservoir won't dump out), remove the dummy hose, and quickly install the original return hose. Make sure to slide the hose clamp back over the end of the hose. Wipe up any drips to accurately check for leaks later. Fill the reservoir only to where indicated on the dipstick on the cold fill line, and install the cap. Start the car and turn the wheels back and forth several times. Shut it off, and make sure the fluid level is still where it should be. Mine stayed the same, proving I introduced no air to the system during the flush. Even if air was introduced, starting the car and turning the wheels back and forth several times is a bleeding process. I would rather not have to bleed it because some systems can be tricky.
Reinstall the coolant overflow tank if you removed it, and install the two 10mm nuts. Lower the vehicle back down.
Fluid colors: On the left is the original fluid, the middle is the last flush color, and on the right is a small sample of the current fluid color. Very much like the new fluid color.
I used 2.2 quarts during the flush. The two on the left is the old fluid put back into the containers, and on the right is new fluid. You can see that the color of the new fluid is not clear, it's just like the color that's in my reservoir.
So, that's how to flush a power steering system on a 3.8L. This should increase the life of the components such as the pump and rack and pinion. For what it's worth, ($10-$15) this is a great way to maintain your power steering system. It may even give you .1 better mpg due to better lubrication and less heat created.
