Power Steering fluid max/min

[DIYspanner]

Its just something I'm curious about.

The reservoir holds about 750ml but the gap between min and max levels is only about 8mm. In this case a Nissan Primera, although my old 45TD was the same.

Its the design of the system obviously but why make it so the required fluid level has such a narrow margin?

 

[Hugh Jaleak]

Just my thoughts, but on the Rover, the fluid seems to increase in volume with the engine running, probably as its being circulated around the system, and returned to the reservoir. Too much and it may escape the bottle, too little and possible risk of air being drawn into the pump resulting in cavitation.

 

[DIYspanner]

That was certainly the case with my 45TD.

Just seems silly, 8mm difference between max and min levels!

 

[Hugh Jaleak]

Believe it or not, the reservoir on a truck isn't a great deal bigger, probably holding a couple of litres at most.

 

[Burnerman]

I'd guess they have to give you - as an owner or mechanic- a reference as to how much fluid the system contains.
The fact is, the fluid level won't change in normal use, but if the max and min markings are close together, you can at least see if there is a leak and can do something about it.
It's curious though, changing the fluid isn't recommended throughout the vehicles lifetime - although it is subjected to temperature extremes and metallic particles!
John

 

[DIYspanner]

When I had the leak on my 45TD, once the fluid was slightly below min, the effect on the steering was obvious. It felt "notchy".

The leak was on the pump and I never did get the leak completely stopped although automotive silicon around the body joint did reduce it.

The PAS on the 45TD used Dexron 3, but the Bora, my present motor, uses a different spec fluid.

 

[Burnerman]

So long as the reservoir actually has fluid in it - with the engine running and the steering operating - all should be well. Lumpiness usually indicates impending rack problems!
John