My power steering pump makes a cavitation noise upon startup that I can't seem to explain or fix. It started making the noise about 2 years ago during cold starts, with temperatures below about 5 deg C, (40 deg F). It lasts for a few seconds, and then the cavitation noise stops, although the pump continues to make a slight whirring sound. The steering performance does not seem to be effected in any way.

I changed the reservoir assuming the filter was clogged, but the filter did not look dirty and the symptoms did not improve with a new reservoir. I then changed the pump and it also made no difference. I then changed the return hose (reservoir to pump) and that made no difference. Each time I flush the fluid with new ATF+4. The system does not loose any fluid and there are no foam/bubbles in the fluid other than some very small bubbles after it cavitates during startup. I took it to my local trusted mechanic and he had no suggestions beyond the clogged reservoir screen. Same story with the mechanic at the dodge dealership. I changed the reservoir for a second time and again it made no difference.

It seems the flow rate back to the reservoir is high, but I haven't been able to confirm its abnormal.

Any thoughts would be greatly appreciated. I'm stumped.

 

Given the parts you’ve already replaced, the issue is narrowed down to either air that is trapped in the system or it’s a problem with the pressure line, rack, or cooler (if equipped).

When it comes to bleeding ps systems, I find pulling a vacuum on the reservoir while bleeding is the most successful. I have a selection of rubber corks that I installed fittings in my so I could hook up my manual vacuum pump. I’ll put at least 15 in-Hg of vacuum on it, then slowly turn the wheel with the key off. When I see the vacuum drop below 10 in-Hg, I pause until it recovers back to 15, then continue turning. Repeat until you’ve cycled the wheel at least 10 full turns stop to stop.

As to testing the line, rack and cooler, a pressure tester is your best bet, though I’m not sure any stores will rent them. You’ll have to check.

 

Thanks Gumby. I will try to bleed under vacuum.

Cheers

 

Had a similar problem on an older Honda Accord. I read that an o-ring on the power steering pump shaft could be worn, allowing air to enter at the pump suction. The o-ring would swell & seal after it warmed. The repair was to simply disassemble the power steering pump and replace the o-ring. However, I sold the car before I could make the repair.