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Just a quick question to ensure that everything is correct:

On my 2009 Opel Astra I want to do a preemptive steering fluid replacement as the original fluid is quite old and is becoming dark. At the moment I do not have steering issues, but I was told that dark steering fluid indicates a stale fluid, causing excessive wear on the steering system.

Frowning the work and time involved, I do not plan to flush the entire steering system (pump, hoses, rack etc.). My plan is to suck it out of the reservoir, using a vacuum pump and a clean hose. After that I will top it up with fresh fluid bought from the dealership.

I am aware that I will have an certain amount of old fluid in the resulting "mix", on the other side the steering fluid should be "refreshed" enough to warrant this shortcut.

My question now: Do you think that my approach and my guesses are reasonable?

Update:

Turns out that the fluid is supposed to be dark, as it is emerald-colored when fresh. The old fluid, over time, turned olive green. I was able to extract ~300ml, the manual says that total capacity is 700ml. So I would need three runs to renew it to ~81% new fluid. Three runs, as the fluid gets sold in 1 liter packages.

  • What type of power steering fluid is in your system? If its hygroscopic like brake fluid then it will absorb water over time, and a full flush would be best. – Criggie Oct 6 '18 at 3:31
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    @Criggie the name is "pentosin chf 202", there is no indication of the base type – Martin Oct 6 '18 at 10:19
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Go for it, you should be at least 50:50 to new V. old and most likely better.

If you check a decent workshop manual it may say the total capacity for power steering fluid, in which case you will be able to know for sure.

Either way, it can only help.

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What you're suggesting should work well enough.

While I get your want to not do a complete purge of the power steering system, you could do one more simple thing which would probably get your car to about 80-85% of the fluid changed out. If you jack the car up and put it on jack stands (supporting the front end), then disconnect the return hose at the power steering pump, allowing it to sag down into a catch basin, then turn the steering wheel lock to lock several times, you'll end up purging the system of quite a bit of the fluid. You don't even have to run the car to do it. If you did run the car, you could run it dry the same way and do a complete fluid exchange. With it up in the air, you're not putting a lot pressure onto the steering system, which means no strain. To do it right, even with just purging out the reservoir, you'd still want to ensure there's no air in the lines and the best way to do that is to run the steering lock to lock several times with the tires up in the air.

  • I like your arguments, unfortunately the engineers made it difficult for me. The two hydraulic hoses use one combined connector to connect to the steering pump. The hoses at the steering gear are single, but are supposed to get a new seal ring. The workshop manual suggest prior removal of the front axle body for good accessibility. All this combined is too hairy for me, so I'd go the lazy route. – Martin Oct 5 '18 at 21:06
  • @Myself - That really sucks. Most of the power steering systems I've seen are really easy on the low pressure (return) side. Usually a hose clamp holding it on. Be that as it may, I don't think you'll have any issues with your idea. You may want to drain it the best you can, fill, run, then drain it again. Get your level up to ~75% new fluid. – Pᴀᴜʟsᴛᴇʀ2 Oct 6 '18 at 2:10
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Yes, this is a common practice for changing fluids when draining the system is impractical or impossible. To get more of the old, dirty fluid out, you can repeat the process several times, running the system to mix the fluid in between, though this has a diminishing return. A good process for doing this with power steering:

  1. Jack up the front of the car slightly to get the front wheels off the ground.
  2. Drain as much fluid as you can from the system.
  3. Fill with fresh fluid.
  4. Start the car and turn the steering all the way to one side, then back to the other, several times.
  5. Stop the car and check the fluid. If it's still visibly darker than fresh fluid, repeat from step 2.
  6. Set the car back down on the ground, you're all set.

Side notes:

  • Never put any part of your body underneath a car that is only supported by a jack! However, in this specific procedure, you don't need to be under the car at all, so jackstands are not strictly necessary. Be aware that the jack can fail or slip.

  • Different cars use different types of fluid for power steering (Power Steering fluid, Automatic Transmission Fluid (ATF), Central Hydraulic Fluid (CHF), etc). Make sure you're getting the right stuff for your vehicle.

  • A turkey baster is a low cost option for removing the old fluid.

  • Did you read the answer by Paulster2 before posting? – Solar Mike Oct 5 '18 at 22:25

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