Mk2 1.6 Petrol Hatchback power steering pump noisy on full lock

[AntonovAN12]

As the title says. The power steering pump will squeak when the steering is turned to full lock in either direction. It does not make any noticeable noise during normal driving.

The fluid is at the correct level in the bottle. 

When I bought the car earlier this year I did a gradual power steering flush. With the engine off, I emptied the bottle using a large syringe and tube, then refilled with the correct green power steering fluid. I repeated this several times, driving as normal for two weeks between each fluid change. The bottle holds around 165ml, so this was a total of six fluid changes once a fortnight over three months. Using this method, no air enters the system, and contamination is removed each time the bottle is emptied.

At the start of this process, the fluid looked black. By the time i had used the full litre of new fluid, it looked a lot cleaner. As far as I can tell, Ford did not publish a service interval for the power steering fluid, intending it to last the useful life of the car. I assume that the old fluid had been in the system since the car was built.

However, the pump is still noisy at full lock. Is this normal for these pumps? From what I have read, pumps on some makes and models of car are noisier than others.

[FatHead1979]

When you say 'on full lock', I hope you don't mean that you're holding it on the steering limiter! 

[JW1982]

Holding a hydraulic power steering system at "full lock" should be avoided at all times.

At full lock the hydraulic piston of the steering rack is at the end position and can not move any further. The hydraulic powersteering pump however generates pressure. To prevent the power steering pump from jamming (hydrolock) the steering rack has 2 small overpressure valves (1 for each side) to prevent damage to the system.

At full lock the hydraulic pressure of the power steering pump is forced through the small overpressure valve. On one hand this puts excessive stress on the power steering pump and can cause excessive noise from the pump. On the other hand the fluid being forced through the small overpressure valve generates a lot of heat and can also cause excessive noise.

[AntonovAN12]

Thanks for the replies.

I don't hold it on the limiter, but occasionally end up touching the limit when trying to get out of tight spaces. That is when I have noticed the noise. I back it off again as soon as it reaches the limit.