power steering foaming
 

Hi all,

I'm really scratching my head about an issue I have with my power steering. It foams and causes the fluid to spill over the tank on top of the pump. I have cleaned and checked the whole system and there are no fluid leaks apart from the spill over. It is as if the system was sucking air but not leaking fluid under operation. When I bled the system with a clear hose running from the bleeder on top of the steering box to the tank the fluid was first normal and after a few seconds started becoming foamy. So it sucks air during operation.

Would anybody have an idea where that air could come from without leaking any fluid?

Of course I made sure that the fluid level is ok so air is not being sucked from the tank.

Thanks in advance for the help!

I ran into this once and solved it by cleaning the filter in the PS tank.

Sometimes these get tossed out by a previous owner. Fastlane will have these and they should have a photo of one so you can see if yours' is still there.

Only one thing can cause foam in a hydraulic system and that is air. If your system sucked air when your fluid is low you will have to bleed the system and then maybe bleed it again.

Try running the car without the fiber PS filter and see if there is any change. A dirty filter can also cause this problem as can a faulty gasket on the PS steering tank top.

My 108 has had this problem now for years and even after having the pump rebuilt, it still does it! Filter was replaced at the same time. Right now, especially since I never drive the car, I just leave it really low and tolerate the hard steering putting it in and out of the shop.

Anxiously awaiting answers....

Regards,

David

Is the return hose in good shape? Is the gasket on the reservior cap sealing?
I followed this procedure for flushing and it solved the foaming problem:

Flush Power Steering Fluid Exchange

You'll need a helper. The steps are rather simple.

1. Lift front tires off the ground.
2. Disconnect the ps return line at reservoir, drain ps reservoir.
3. Plug open connection at the reservoir.
4. Secure the return line to a generously-sized container (at least one gallon). If needed, add a length of hose.
5. Fill reservoir with new fluid.
6. Line up your bottles of new fluid for quick pouring.
Here comes the fun part...
7. Have helper turn car on, and immediately have him go through full range of steering motion (left and right) all the while you are trying to keep the reservoir filled. Shut off car after about 3 quarts are run thru the system.
8. RE-CONNECT RETURN LINE.
9. Clean up mess.
10. Top off fluid.
11. SLIGHTLY CRACK BLEEDER FITTING ON TOP OF BOX WITH CAR RUNNING AND HELPER TURNING WHEELS UNTIL ALL AIR IS EXPELLED AND FLUID STARTS TO COME OUT.

The front tires must be off the ground so the system is unloaded, otherwise a lot of fluid is forcefully pumped out. The return line must be secured to prevent a big mess. Keep at least a couple quarts of ps fluid on hand. The helper must know what they are doing.

This has also been discussed not too long ago here:
http://www.peachparts.com/shopforum/vintage-mercedes-forum/279768-power-steering-pressure-build-up-reservoir.html?highlight=foaming

Basically, it's caused by a leak somewhere in the return area. A leak will allow air into the hydraulic system, which then froths the fluid when it's whipped around in the pump - kinda like mayo except using air versus water as the emulsion fluid. A leak the size of a pin tip can cause this. My steering gear box leaks on the high pressure side a bit, not too badly; and it doesn't foam since the leak is on the outlet vs inlet. I just run low on fluid due to it. You can try the bleeding procedure but I would replace the inlet hose & make sure it's clamped on well first.

This is some good info. As our cars age this is going to be a problem for more and more people.

Make sure you let us know all that you did and what you found.

What do you call the inlet hose? The low pressure one?

Yes, the low pressure one (return line).

Regards,

David

I was a bit confused on the return line being called inlet. Yes, mine is all greasy and I suspected this could be the only place where air is being sucked but I would have imagined seeing it drip under operation which is not the case. I'm going to replace it.

Thanks all for the help.

The hose has a vacuum in it during operation, it's more likely to leak when the vehicle is sitting than running. If you clean the hose and it becomes greasy again, it likely has several pintip-sized leaks in it. You may have a leak in other places (like the gearbox or pump) but this is the easiest & cheapest part to do to rule out the cause. No filter in the pump I suppose could affect flow and cause issues as well, but not that frothing you're describing.

some times the relief valve stick's .and the suction is greeter than it need's to be to the feed the pump and lines and seals are put to the limit.

I just replaced the return hose and the system is still sucking air from somewhere during operation. The system is not leaking from anywhere during operation or engine stopped. Where can that air be sucked from?

280s 108
 

i have a identical problem ; i replaced the pump & filter but the faultiis very much there . Pressure in the reservoir and spewing of fluid

mak

there's pretty much only 1 other place that I can think of - the steering gearbox.

Pinhole leak on other steering hose or around the hose fittings, perhaps?