Don't ignore a squealing noise from the steering

When I turn the steering wheel on my 2004 Opel Astra there's sometimes a squealing noise that seems to be coming from the front of the car. Is it something I have to worry about, and how can it be fixed?

Thandiwe

There are several possibilities, Thandiwe, some relatively harmless, others more worrisome.

It can be that there is too little hydraulic fluid in the power-steering system. The fluid, under pressure from a pump, is used to provide the assistance when you turn the steering wheel.

Check whether there is sufficient fluid by locating the power-steering fluid reservoir in the engine compartment. The reservoir will either have high and low marks moulded into its transparent plastic body or a small dipstick sprouting downwards from the filler cap. To check the level of the fluid in the reservoir, park the car on level ground and, with the engine idling, slowly turn the steering wheel from lock to lock two or three times.

Then set the front wheels to the straight-ahead position and switch off the engine. The fluid level in the reservoir can now be checked - it should be between the upper and lower marks.

This is also a good time to get some of the fluid on a white paper-towel (use a finger if necessary) and smell it while looking for unnatural opaqueness or signs of solid matter.

A burnt smell is a danger sign. Power-steering fluid should really be purged and renewed at certain intervals, but that is a job for a workshop. If the power-steering fluid needs to be topped up frequently you have to get the system inspected for leaks, perhaps at a seal or at a union on one of the hoses.

A noise like a high-pitched wail can be produced if the drive-belt for the power-steering pump slips on its pulleys when under stress. This is less common on modern engines using a multiribbed serpentine drive-belt than it was on the older cars using a single V-belt.

The V-belt needed periodic adjustment to take up unwanted slack; a serpentine belt usually has automatic tensioners and if these are functional the belt should not develop slack, but if it starts slipping it's time to replace it.

The third kind of power- steering noise can best be described as a spine-chilling screech, and it comes from a pump in its death throes. Although normally reliable and long-lived, the hydraulic pump will eventually wear, especially if the fluid was allowed to become dirty or degraded, or the wrong type of fluid was used when topping up.

Don't expect a reconditioned pump (not to mention a new one) to be cheap, but the alternative is a total loss of power steering on the car, plus probably other consequential damage.

It's worth noting that wear in the thrust bearings inside the top mounts of the McPherson struts (used on the front suspension of most modern cars) can mimic a power-steering noise very effectively. Like a power- steering noise it will only appear while you are turning the steering wheel, because that's when the struts rotate to allow the front wheels to swivel.

The noise produced by a worn bearing in a top mount can be anything from a dry scraping sound to a rumbling whir as the steering wheel is turned. You can pinpoint a worn bearing by getting someone to put his hand on the top mount where it protrudes through the front wing into the engine bay and feel for roughness as you turn the steering wheel from side to side. Top mounts can be replaced, but it's not a trivial job.