coolant flushing, refilling

[Brett Dikeman]

So I finally decide to tackle changing the coolant, which looks
pretty disgusting, and sure enough, when I drain it, it comes out a
very nasty dark brown.  Ugh.

So fill it up with fresh tap water, run it for a while, drain that,
comes out still pretty brown/green.  Repeat.

I'm finally getting something pretty reasonable-looking, but I being
to wonder if I'm not getting all the coolant out; I'm draining from
the bottom aux radiator hose, which is supposedly the lowest part in
the system- yes, engine is fully warmed up, yes, the ignition is on
and the temp set to HI.

Each time, it takes about 4-4.5l of water to fill up the system, and
it doesn't seem like the car sucks all that much down- I was
expecting to have it settle with the car off, start the car, have it
suck the reservoir down, and I'd have to add some more- nope, not
really.  Maybe a little..

After running the prestone coolant system flush, I fill up with fresh
water again, and as per the Bentley, let it run waiting until the
stage II fan kicks on, add coolant as necessary, and move on.

Never happens.

I get a little spit up(this happened a couple of times before, and
only once), but instead of the fan immediately kicking on(as usually
happens after the slight spit-up), it stays off.

And stays off.

Coolant gauge stays straight up, pretty much the entire time, and
next thing I know, I've got a bubbling geyser.  Crap- the car is
boiling over.

Shut it off, flip on the afterrun circuit 'hotwire' switch I have,
and dump water in.  Capped it, turned on the engine, and let it run
to even everything out.

It never boils over with the cap on, so my thought is this- is the
Bentley procedure really only for when you've got water AND coolant
in the engine, not just water?  Perhaps the t-stat is sticking, or is
the wrong temperature?  Stage II temp sensor wrong temp or sticking?

As a side note, I'm embarrassed- the coolant system was clearly
neglected by yours truly.  Even after 4 flushes, I'm still getting
scale and rust bits, and only now is the water coming out a
reasonable color...egad...

Brett
'91 200q20v
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