When I fire up my 80 Pickup in the colder months, it makes a strange sound. I think it is linked to my steering box, it sounds like a strange hum/vibration that is loud. The sound fades when it heats up. It gets louder when I move the steering wheel when I start it.

Thoughts? Thanks for any help.

 

Power steering pump. Either it's old and tired, or the fluid is old and tired, or it's the wrong fluid. Flush it with the correct stuff (Dexron-type ATF, not "Power Steering Fluid") and see if that helps. Do you have belt squeal too?

 

This is a day late and a dollar short, but what you're hearing is called 'cavitation'. Basically a fancy term for air in the pump. In very cold weather (-20C) a combination of fluid contraction, drain back, leaky seals etc causes some or all of the fluid to drain/sucked out of the pump. The whining sound is air in the fluid being forced out (best explanation in layman's terms I can give you) As a semi-retired millwright I've heard that sound lots, if its all the time you got problems. Other than it sounding like a yowling cat and a lack of lubrication to a degree, there's really no harm (If it were a new truck I'd be beating on the dealers door though!) You can fix it all up, do it now or wait till it breaks, or do nothing other than what moroza suggests. My 83 does it, my 04 Taco has done it for the last 7 or 8 years and its got 480000kms on it. But our 10 Yaris doesn't but its only got 68000km. Again if there's no leaks just change the fluid and drive it. Be aware it'll really whine after changing the fluid because of the air in it.


I have to edit because I don't feel I really explained it good enough. Cavitation is caused by a pressure difference which allows a vapour (air in this case) to enter a fluid in the form of bubbles. As the pump runs the bubbles are forced to the outside of the pump where they then implode causing noise and vibration. Fluid then rushes into the void left by the bubbles and then causes erosion of pump surfaces the bubble was touching (think hydro machining). This sounds kind of scary but we're only talking microns here, however if left unchecked continuously it will cause pump damage (mostly shot bearings) usually due to a un-balanced rotor/vane assembly. A cavitating water pump (industrial ones) will sound as if someone is beating it with a sledge hammer and you'd swear the pump casting just broke, and they will also usually be hot adding to the vapour problem. Cavitating hydraulic pumps (and that's basically what a power steering pump is) don't sound as bad, oil cushions better and the bubbles are much smaller. Yes fluid of too high viscosity will cause this too. This is very common of hydraulic pumps that operate in cold conditions and they should be allowed to warm up before loading the pump.

 

I was under the impression that cavitation was bubbles of vacuum, not vaporized fluid or air. The resulting mechanical erosion can in some cases be a serious problem, mostly with diesel cylinder liners (this is why many diesels, especially bigger direct-injection ones, call for anti-cavitation additives. On some engines I have actually heard them get noticably quieter when normal green antifreeze was switched to the diesel-specific stuff). I suspect that mechanical erosion is a non-issue with a small oil pump, but the lack of lubrication - such as from foamed-up oil - would be more of a problem.

 

I've not heard of the vacuum thing...Hmmm. But it would be sort of the same thing. I've believe I know what you're saying about the cylinder liners in diesels and if so, have seen it on a big (2000hp) stand by generator prime mover. At the time I thought it was just bad corrosion as it only used water and boron for coolant, but maybe not from what you're saying. Big hydraulic pumps (100hp+) apparently can just explode, not seen it myself, but really old timers have told they have. Yup foamy oil could do it too

 

Cavitation in diesel liners is caused by the liner moving inside the block creating tiny air bubbles in the coolant. The bubble causes the liner to heat up due to no coolant contact in that tiny area of the bubble Then when the flow of coolant moves the bubble on, the coolant boils from the hot area of the liner and this results in a microscopic piece of the liner flaking off It always shows up on the side of the liner that the piston pushes on when coming down on the power stroke.