Bit of a daft question this, but anyway.
When the car is sitting idling, it makes long ssssssssssss sounds for a period of about 10 or 15 seconds every so often, in a regularish cycle. This isn't the usual pssssst-click accumulator cycle noise, more a sustained hiss.
The hydraulics seem fine, car is rising smoothly, and brakes and steering are as they should be, no ( ! ) or STOP, etc.... This isn't a problem as such, I am just curious as to what is actually going on in the system when this noise happens.

When driving, my old XM would make that noise briefly, when taking off, or when the brakes were pressed occasionly, etc... but it never had sustained periods of it like this.

If it's any bearing, I recently tightened the pump belt, as it had been slipping and squealing...

Anyone hazard a guess ?

Hi there, mine does the same at idle until a rev it a bit then i guess the accumulator has enough pressure to be getting on with.
The fault on mine is the front solenoid block pressure is constantly being lost around the valve. If you disconnect the plug on the front solenoid valve it should hold the system pressure for longer.

Rouben.

Hi,

Do you mean the hydractive valve ?

Cheers.

Mine does the same and I appear to have an excessive ammount of fuel being returned to the reservoir, meaning something somewhere is worn, but it also drives OK. See my post before this one 'Where is all the pressure going'.

Peter.N.

Yes its the Hydractive valve, if you look under the car at the valve you will see a rubber return hose that comes off the end of the valve. I think this joins the similar hose of the rear hydractive block and goes back to the reservoir.
What i did was to disconnect the return hose from the front and block it off then connect a clear plastic tube to the solenoid return at one end and the other end placed in the reservior filler hole.
Now with the engine running you can see if fluid is flowing back to the reservoir, it shouldn't do!.

Rouben.

Mine does the same and I thought it was cured after I changed the pump. It is back now. With the old pump it would even go on forever. It normally came up after starting the engine. Once it was warm it normally disappeared. I am still not 100% convinced what it is, on my car too, everything otherwise behaves pretty normally. I usually rev it until it stops.
Has anyone changed the regulator and then made any dicoveries?

Michael

Might be a worn flow distributor, I recently saw an XM that was continuously hissing -kind of loud- till you turned the steering wheel even just a little bit...

George

Turning the steering wheel stops mine but that seems to be because the demand for more fluid has lowered the pressure and caused the pump to fully cut in. You can also stop mine by just bliping the throttle, this charges the accumulator sphere but at tickover the pump will not keep up so in a few seconds it starts hissing again.

Peter.N.