Mercedes ML350 - loosing power steering

[decosta]

I have Mercedes ML350 2007 model with 134000 kms and since last month I am experiencing some light vibration (sensation) and low humming noise while turning steering, which I have been ignoring it all this long. Two days back I noticed that power steering is becoming hard to turn after 15-20 minutes of driving, before I loose it completely I thought of checking here first before taking this to workshop (if needed). Thanks everyone for reading this and helping me, if you know anything relevant. Cheers.

[gautam]

Hi decosta,

The symptoms you describe are related to the quality of the power steering fluid, and possible damage to the pump caused be dirty fluid.

Because of the small volume of fluid in the steering system, the deposists that form as a reult of the the degradation of the fluid have nowhere to go, but into seals, valves, and the pressure regulator in the system.

The additives in power steering fluid break down after a few years, meaning that the fuid is no longer able to lubricate the pump and steering rack, which is why it gets harder to turn as the system heats up, because  the moving parts expand, and the fluid cannot lubricate them because the additives in the fluid no longer work. 

The whining noise could be from damage caused to the pump due to poor lubrication, or fluid being forced through small passages that are partially clogged by sludge in the fluid. My guess would be that the pump is already damaged, but it may be possible to save the pump by doing the following:

1.) Add about a cup full of engine flush to the power steering system, and allow the pump to circulate the old fluid (with the engine flush added) for about thirty minutes or so. Turn the steering from side to side every few minutes to allow the engine flush to dissolve the sludge in the system.

2.) After about thirty minutes, let the system cool down, and drain the fluid from the reservoir. Add new fluid of the correct grade and type, and let the system run for a few minutes.

3.) Drain the fluid again, and repeat. You may have to drain and refill the reservoir several times until all the old fluid has been replaced, but this should solve the problem. If the pump remains noisy with new fluid, it is damaged, and you will have to replace it unfortunately. Hope this helps.