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2005+ power steering reservoir, and p.s. system problems. A look inside . . .

9K views 6 replies 3 participants last post by  plain OM 
#1 ·
I’ve been changing the power steering ATF in my 07 regularly using a battery filling bulb and noticed that I can’t completely empty the reservoir – the bulb tube doesn’t go further down than roughly the perimeter joint near the bottom.

I also was puzzled by recent power steering problems reported in the forum where aeration and overflows were not readily resolved by changing o-rings, the adapter, clamps or hoses.

This led me to wonder how the reservoir is constructed inside, and what impact it could have on the system.

I retrieved two 2005-9 Outback reservoirs from a recycling yard, and opened one to see what’s inside. The result might suggest that the reservoir could be a contributor to problems not resolved in the usual manner.

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This model reservoir was used in 2005-9, and a very similar one was used in the next generation until the change to electric-assisted steering.

Product Yellow Machine Metal


Next is the upper part separated just above the perimeter joint. Here we see the inlet tube and three sections that make up the bottom part.:

Auto part


The next three photos are close-ups of the three sections (chambers), two of which have screen filters on the bottom.

Water Auto part


In the last photo above, we can just see, through the center chamber round opening, a similar screen below the center chamber. There’s also a black gummy substance on top of the chamber.

The following two photos show the position of the cap’s solid tube when the cap is in place (based on measurements). The tube blocks the opening in the top of the center chamber. Consequently, fluid being pushed into the reservoir from the inlet tube is forced down through the screen filter into the bottom of the reservoir.

Fuel line




A further separation at the perimeter joint reveals the path of the incoming fluid from the inlet pipe to the center chamber. All circulating fluid has to pass through the small round opening from the inlet tube into the center chamber.

Yellow


The final disassembly was to remove the bottom to reveal three separate filter screens.




Some observations:

Incoming fluid from the inlet pipe goes into the center chamber, and with the cap tube in place, can only go down through the screen filter of that chamber. It goes into the bottom of the reservoir where it is drawn through the outlet tube to the power steering pump. That one screen is the only filter for fluid returning from the power steering rack and control valve to the power steering pump inlet. The other two chamber screens filter fluid that is in the reservoir above, as when filling the reservoir.

The reservoir cap is vented. It’s a small opening that normally will prevent any pressure or vacuum build up in the reservoir due, for example, to temperature-related expansion or contraction of the ATF.

The power steering system is made up mostly of solid materials – the rack, the tubing, the pump etc. There are no areas where the internal volume can change significantly. Moreover, fluids, including the power steering ATF, cannot be compressed to any degree. For every ounce/ml of fluid pushed out of the power steering pump toward the steering mechanism, an equal volume has to return to the reservoir and back into the pump on its inlet side. Even when the steering is being turned and fluid is pushed into one side of the rack to assist with steering, the same volume of fluid moves out of the other side of the rack. Consequently, the level in the reservoir should not change in normal operation.

The design of the inside leads me to wonder what would happen if the cap vent was blocked, or if the center chamber screen was clogged. In regard to the latter, there shouldn’t be a lot of material coming into the chamber from the rest of the system unless there’s a component failure. However, when the cap is off, the center chamber is open to the upper part of the reservoir, and to whatever is there (e.g. that black mass on the top of the chamber). Moreover, the chamber opening is directly below the fill opening of the reservoir, and debris can get into it while replenishing, or if the cap is left off for some time.

Could a clogged screen cause or exacerbate some of the problems attributed to leakage at the pump return fitting, o-ring, or hose?

Would it be prudent to remove and back flush the reservoir when replacing the o-ring, or better still just replace the reservoir, in addition to replacing the o-ring, when there’s aeration or unexplained overflow problems?

Food for thought . . .
 
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#2 ·
Ecellent write up (as usual) Plain, thanks!

I looked up the reservoir cost for my 08, it's about $42. I think it's worth a try before next winter (all quiet now).

I still question the pump inlet and new red oring as several people that have reported it cannot be completely tightened with the one bolt design.
 
#5 ·
. . .
I still question the pump inlet and new red oring as several people that have reported it cannot be completely tightened with the one bolt design.
If the 1 bolt design is not tight enough, maybe make a thin gasket for it?
Or wrapping it where it comes together with teflon tape to seal it from the outside and try that for a couple days just for troubleshooting purposes?
I might be wrong, but at this point I don't think the one-bolt design is a significant factor unless the pump inlet "connector - pump assembly" it holds down, or the top of the pump housing, is cracked, warped or nicked, and that could happen with a two bolt hold-down as well.

It seems to me that the o-ring need only be fairly snug between the connector and the pump (i.e., not necessarily "flattened"). The plastic version of the connector has a metal liner where the bolt passes through. The liner limits how far down the bolt can be tightened, and with a properly-shaped connector, that should bring the connector down sufficiently against the o-ring to properly snug it against the connector and the pump housing. Trying to further tighten the bolt only risks mis-shaping the connector or stressing the bolt. (There's also a metal version of the connector and, again, that would limit how far the bolt can be turned in.)

With a good o-ring, intact connector, vented reservoir, and an equal volume of fluid flowing through the system, I believe there would normally be minimal negative pressure at the o-ring. Consequently, if there's still a foaming problem, the root cause might not be the o-ring or connector, and if the hose and clamps have also been replaced, then the reservoir or other parts of the system probably need to be considered.
 

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#6 ·
I agree.
When I first started messing with this issue, I bought a oring and the elbow piece to have on hand incase I needed it.
When I took off the plastic elbow piece and inspected it, it looked perfectly fine and by how snug the oring fits around this piece, It seems that there's no way the elbow piece could be a issue since all its sealing is from the oring. So I returned the $30 elbow piece.
I also replaced the clamps on the old hose that the rubber was very hard and when all back together, I still had same problem.
So I bought a new hose and put the origanal clamps back on and still having the same issues..

I'm just running out of options..
Will be putting back on the cleaned resivour in the next couple hours and see what happens.

I'm gonna look at the rack while I have the car in the air and everywhere else I can that might be sucking in air. I seen no leaks when I looked around the first time, but I'm getting desprate now..
Why such a simple setup being the most difficult to figure out..
 
#7 ·
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