Hi, I found the forum and it looks like there's some knowledgable people contributing here. It's not like the other boards where every reply is take it to the dealer. If I wanted to take my vehicle to the dealer I wouldn't be looking here. Anyway, I hope I can help around here too.

I am having a weird problem that is starting to get frustrating. I'm hoping someone here can give me some advice or some more ideas. I'll explain it all from the start.

- A couple months ago I was about 100km from home when I started to hear a whining sound while the vehicle was running.

- I checked the p/s fluid at a gas station and it was low so I added regular p/s fluid and I drove it the 100km home with no improvement in the noise.

- The next day I figured out that I should have used MB fluid or the right kind of ATF. I figured it was making the noise still because I used the wrong fluid, so I emptied the system and filled/bled with Dextron ATF with no improvement.

- I figured that I must've ruined the pump at this point so I drained all the ATF, replaced the pump, and filled with the MB fluid all to no avail.

- At this point I decided to replace the rubber o-ring between the pump and reservoir. Again with no improvement.

- It was like I couldn't get all the air out of the system, so I decided to replace the steering rack. I figured it had a blown seal or something so it wasn't pushing the air out.

Well I finished that job this past weekend and I couldn't believe that there was no improvement in the noise after I took it for a short drive last night. I've only driven it 3-4 times about 1km each time as I'm afraid to ruin another pump. I want to start driving this vehicle to work again though. I've ordered a new reservoir and it should arrive tomorrow, so I'm going to try that next.

The system is not that complicated and after I install the new reservoir I will have replaced everything but the hoses. I inspected the hoses when I replacing the rack and they seem ok. I also checked that the return line was not collapsing while the vehicle is running.

However, after reading a few posts I am beginning to wonder if I am looking too closely at the p/s system.

Do you think I have to drive it for awhile to purge the air? I have drained it completely three times after all. If so, how far do think I'll have to go to see an improvement?

Also, if the serpentine belt tensioner was messing up would it put extra strain on the pump causing it to whine? It gets louder when you turn left or right.

I am totally open to any other comments, ideas, or suggestions (aside from taking it to the dealer).

Well the reservoir fixed it.

I'm thinking it may be the lid that caused the problem now that I've checked out a new res and an old one side by side. If it wasn't venting I don't know if it would let the system bleed itself. My old lid looks kind of bad compared to the new one, but I thought it and the res were fine just by looking at them. A cleaning of the lid might have fixed it though.

Either that or the filter in the res was too plugged and the fluid was getting air in it. I don't know what it was, but I'm happy I fixed it.

If anyone hears this noise and finds this in a search I'd advise them to change the reservoir and o-ring before anything else. I found out the hard way.

Wow, bummer replacing the rack and it was not the problem. I replaced a rack once on a Ford Probe and it was not something I want to do again anytime soon.

Anyway, I have been thinking my power steering pump is kaput because it is making a whining noise. I put some Lucas Power Steering additive in and it has quieted down the noise considerably but not all together. I was thinking a new pump is in order but your post has me thinking that it could be the reservoir and not the pump. Tonight the hose to the radiator popped out causing fluid to leak all over the road with no power steering on the way home. This could be due to the thicker Lucas fluid when it is 14 degrees F out today.

I have a 1999 ML430 120K Miles

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99 ML430