Follow you is tough with that question.  Nothing will come out the
reservoir neck, it'll all be on the ground, before you have a chance to
turn the car off.

If you cut open the boot(s) at this point, you will just pump the entire
system empty.  You can't pour fast enough from quart bottles to even top
off the reservoir.  No power steering at all.  Huge puddle of oil under
car.  Then it'll just all gravity drain out the bad seal(s) as you drive
along.  Helps build upper body strength, though.

Quit futzin' around with theories and change the rack.

Rob

cool, so in actuallity i could test this theory by cutting the boots off,
then running the car with the correct reservoir level, then shut it off and
see if the leakage comes out of the rack seals or the reservoir.
are you following me?
i think this makes sense after reading your last response.

It bleeds back into the rack through the compromised seal, and as
someone added PS fluid when it was low, the system is now overfull.

NO.

Only a backup of PS fluid - someone added it at least once & probably
more, it didn't all leak out, so when at rest it has to go back
somewhere into the system when the system pressure equalizes... the
reservoir is the high spot, that's all.  If the boots aren't torn, it
will just overflow the reservoir, and the worse the seal gets, the
faster it will back up.  Not uncommon in Taurus & Sable - they have
really good boots!

 i know i will have to replace

NO.

Rob

no, no, fluid is phisically coming OUT of the reservoir through the cap vent!
!!!!!
this has to be some kind of clog or backup (?) i know i will have to replace
the rack, but will the fluid still come out of the cap when im done?

It bleeds back into the rack through the compromised seal.

Rob

thats all well and good, i have seen plenty of leaky racks that fill the
boots up with fluid, but why the heck does the fluid come out of the
reservoir when i shut down the engine???

I've seen the Taurus several times come around with low PS reservoirs
that the owner has topped off.  The rack boots actually fill while
driving, draining the reservoir, the driver adds more, & if the boot(s)
doesn't rupture, it overfills the reservoir when shut down, & bleeds
back in to the rack(it's pretty bad by this point).  The complaint is
usually " I keep adding PS fluid, but it doesn't leak out".  If they add
fluid while running, the boot takes on more fluid than it can hold &
blows PS fluid all over the driveway.

Rob

 Rob, his rack is obviously bad due to the leaks. What would cause it to push fluid
out of the reservoir on shutdown? I've seen a lot of racks failed in various ways but
that's a new one for me.

 bbyer, the "check valve" that you referred to is not in the hose. It is an orifice
in the high side port on the rack. Basically a disc with a hole in the center that
goes into the fitting before attaching the hose.

Absolutely.

Time to change out the rack - the seals have failed... you have ALL of
the symptoms.

Rob

the p/s fluid level on this 99 taurus i'm working on is fine when the engine
is running, and the steering works great. but when you shut off the engine,
the fluid slowly comes up and spill out of the pump reservoir. i have never
seen such a thing!
i looked online to see if anybody had had this happen, and alot of people
were saying that it can be cause by an air pocket, but i made sure that it
was bled out, there is no way thats causing this.
I read that there is a problem with the pressure lines. is this true? another
mechanic i know said he changed one on a taurus once because there is a check
valve built in to it and it goes bad, causing this same problem.
 before i  became aware of this i changed the pump and there was no change.
but now i noticed fluid leaking out of the tie rod boots. there must be some
serious pressure build up in the system to blow the rack seals out. now i
guess i'll have to change the rack and the pressure line? the parts guy at
ford said they dont do too many pressure hoses. hes never heard of this
problem.

has anybody here heard of this?