Because it needs a cap/the cap is faulty...
If your power steering pump makes a whining noise as you turn your steering wheel your power steering fluid reservoir is probably empty. The noise is caused when your power steering pump tries to pump fluid that is not there. This indicates that you probably have a leak somewhere in your power steering fluid lines. You can either try to find the leak or simply replace the power steering fluid every so often.
You have a leak. The leak can be from the pump or any of the fittings. You may also have a leak at the rack & pinion.
The steering pump fluid is low (usually the pump will be noisy at this point) or the steering rack is leaking. In either case the fluid is low due to a leak in the steering system.
That means you have a leak. Eventually your power steering will fail (no longer have power assist) and your pump will burn up. You can put some power steering fluid plus stop leak (all in one) in it, but I would also recommend that you crawl under the car and look for the leak.
A loose power steering belt or the power steering pump has failed or the power steering fluid reservoir is empty because of a leak in the system.
Overfilling a power steering system with fluid can cause overpressure. You may cause a leak in your lines or pump.
power steering fluid is fluid that makes the power steering pump work and it goes in the power steering pump under the hood.
Three main risks are associated with power steering leak: 1) Loss of easy steering capability 2) Low amounts of power steering fluid can cause the power steering pump to fail, which is another expensive item 3) Risk of fire with the fluid being dripped on the engine
could be several places, power steering hose, rack and pinion (or steering gear box) or power steering pump.
Remove the plug on the bottom of the power steering fluid pump. Drain the power steering fluid out. Replace the plug to the bottom of the power steering pump. Replace the power steering fluid.
The fluid could be leaking from the pump, hoses, or steering rack. Wash the steering system, then you can see where the leak is coming from.
To fix a power steering fluid leak on a 2000 Mercedes ML320, first identify the source of the leak, which could be from the power steering pump, hoses, or the steering rack. You can replace any damaged hoses or seals and tighten any loose connections. If the power steering pump is faulty, it may need to be replaced. After repairs, refill the power steering fluid to the appropriate level and check for any further leaks.