Help!! 4kq not cooling!!

[bd983@scn.org (SCN User)]

I've been meaning to de-lurk and introduce myself 
but not this way!! The patient is a 1984 4ksq, 165k,
30k on a factory-new motor. We've had the car less 
than a month. Water pump was replaced shortly before 
we got it, well-meaning friend of out-of-state owner
filled cooling system w/straight H20!! It seemed to 
run fine so I delayed rectifying this until the week
end. During that week it heated up on my wife. She
warmed up car briefly while loading kids and related
items, dropped oldest at bus stop (idled +/- 20 min) 
drove 5 miles toward town, temp gauge hit first notch
above halfway, light flashing as she pulled into first
stop. It had cooled down when she came out so she 
continued with her eye on the gauge which hovered around
halfway point the rest of that day (until yesterday!!) 
She said she never heard the rad fan come on at any time!!??

I drained cooling system, added proper coolant and changed 
thermostat about two weeks ago. Hadn't noticed any high temps,
definitely no flashing lights. Heard fan come on when gauge 
moves much above halfway. Everything seemed OK. Until...


..yesterday afternoon. She'd driven (15-20 mi) around town, 
running errands, one brief stretch on the freeway the rest
stop and go. After a while she noticed the coolant light 
flashing (intermittently at first) but since the gauge was normal
she headed home. She didn't make it far - the light stayed on 
consistently and she saw steam from under the hood. She stopped, 
opened the hood and saw steam and "anti-freeze everywhere". Overflow
bottle was empty, she let it cool for a while and tried to call me on
her suddenly non-functional cell phone (Nokia gods and Audi gods in 
collaboration??) Finally someone stopped to help, ran for water 
and filled the bottle. She saw water running out the bottom of the
bottle... She started the car, normal temp, no flashing light and 
made a run for home. Just before our driveway (>10mi) high gauge 
and flashing light. Again she does not remember hearing the fan.

When I arrive home I find less than an inch of coolant in the bottle,
I top it off and watch water drip from a crack in the side of the bottle. I 
run it up to operating temperature. As soon as the system gets pressure
(thermostat open, etc) the leak in the bottle is more pronounced. The 
temp gauge climbs into the danger zone and steam comes out of the crack.
I let it run like this for a bit but *no fan*!! I shut it down when
the light started flashing.

My theories: 

#1 Overflow bottle fails, coolant loss causes overheating.
Is this plausible? The crack is on the front side behind the windshield
washer bottle, it is vertical and follows an inner compartment wall. Do 
these fail over time?? Doesn't explain lack of fan though...

#2 Fan circuit intermittent somewhere causing overheating, increased 
pressure cracks bottle. My incomplete (it was dark, raining and I don't
have a Bentley yet) diagnosis reveals voltage in this circuit only with 
key on, is this normal? In my Rabbit the fan runs independently of
the ignition. I have voltage at socket #14 under the fan relay (#2, right?)
Even at highest temp I could not get voltage to the fan connection. What
is the correct procedure for troubleshooting this circuit esp. the relay? 
(if you have a wiring diagram I have a fax# ;-)) I figure probability in 
following order: fan relay, break in wiring/loose connection, thermoswitch, 
fan motor. Agree/disagree?

My cynical nature forces me to consider this as well...

#3 Head gasket?? No oil/water in wrong places, compression test before 
purchase (me too, Phil!) was 130psi in all 5. Probably not this right...
right!!!???

We're headed into the mountains this weekend and and the snow level is 
down. 
My Rabbit does all right but I was looking for a chance to get the Q in the 
slippery stuff so any hints/suggestions would be appreciated. Replies 
to <clangstraa@ci.everett.wa.us> will reach me more directly as I'm on the
digest at a dial-up connection. Sorry if the line wraps are wierd, this is
not my normal editor.


TIA!!

ClarkL
Bellingham WA
84 4ksq (for safe family hauling)
81 rabbit dsl (for commuting)
70 falcon (for...sale!!)