Power steering goes heavy, then is OK

[Ant]

I have a problem with the power steering, it can be fine, but then all of a sudden can go incredibly heavy, not just when parking but when pulling out of junctions etc, then the next day it can be fine again. It is happening enough now for me to be wary of it.

Does the power steering pump run off a belt ?
Is the power steering pump liable to electrical faults?

I only ask as I hope it is not the whole pump as that will be expensive, but also if it is the pump, how come it works when it wants ? I would have thought if the pump was shot then it would not get better again 

The only thing I am capable of checking is the fluid level and that is OK

Ideas folks ?

[X5Sport]

It's a mechanical pump driven off the engine accessory belt down at the lower right of the engine from the front of the car.  AFAIK there are no electrical connections on the E53 PAS system and Realoem shows it a purely mechanical on the 4.6.

It could be a slipping belt causing the pump to lose assist pressure.  Another cause could be oil/grease contamination of the drive belt.

Although the fluid level is OK, how is the colour?  It should be a nice clear rosy pink so if it isn't it might be a good time to change it.

[Ant]

I will try and have a mooch under the bonnet (if it ever stops raining) and see if I can see any slack belts.
I will also revisit the fluid and check on the colour

Will report back

[Ant]

Google will be the death of me  >:D

Still have not looked under the bonnet (its dark when I get home) I will check the colour of the fuid, but pre-empting things, there seems to be a whine on start up in the morning so I have been searching the Auxiliary belt theory

A: How many auxiliary belts are on the M62 engine (V8 4.6) ?
B: Is this belt what the yanks call the 'serpentine' belt ?
C: Could any slackness be cured by the 'pre-tensioner' thing  :'(

[Ant]

ATF fluid is red and clear, not milky in any way, and is at the correct level.

I cant really see a lot of the auxiliary belt, and I cant really get my hand on it to see if its slack.

so, again, is there only one belt? is it what 'they' call the serpentine belt? can pre-tensioners adjust it, or is that just to aid installation and removal of the belt?