4kcsq cooling problems (somewhat long)

[Tapparoo at aol.com]

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Ok, nothing fancy with this getup, just a stock system.  Drained out old,
VERY green fluid, filled with water from garden hose, then ran until the fan came
on.  No problem, acted normally.  Then I changed the thermostat, hooked
everything back up, filled with water again.  This time, system only accepted about
3 liters (capacity is 8), heated rapidly, fan turned on late, expansion tank
started to fill up, then I heard this awful clicking noise.  Shut off car,
heard gurgling and hissing, then expansion tank dropped way below minimum level.
I used pentosin in distilled water to fill after I changed thermostat.  I
know it doesn't mix with green stuff, so I drained out system again, thinking
that I "lost" a few liters of old green stuff in system somewhere and pink and
green were having problems. Filled with just water again, did same thing.
Next, maybe thermostat was in incorrectly.  Opened up, thermostat in
correctly, but I rotated it 180 deg. just in case.  Now heats up rapidly, only takes
about 3 liters, fan does not turn on, expansion tank does hissing and gurgling
thing again.
Checked thermostat, opens at 87 C like it should.  Is pump bad? (worked fine
24 hours ago) expansion tank bad?  What in the hell is going on here?
Major thanks in advance.
Dan