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you wrote
"Nobody has said anything about the blown radiator (it clearly leaks antifreeze). I'd still like to know if that's the cause of the overheating, or a symptom of the overheating (stuck shut tstat or blown water pump). Again, there's no heat coming into the cabin at all."
Hmmm. Hard to say, and I suspect that's why no answers to that yet.
Certainly an overheating system would build pressure in the radiator; eventually something will give. Possibly the rad blew (if already weak in a spot or two), relieving pressure on the head gasket so it did not blow! But of course if the head was overheated it could have warped and that gasket could let go in the future.
Other failure modes...
Thermostats can stick open or closed, but replacement is quick and inexpensive. If you buy the car, I recommend replacing the t'stat with a known good brand just for security. I like Vernet and Wahler, both avaliable from fcpgroton.com. Vent hole at rim of thermostat goes at the high point when installing. This makes the system self-burping.
Water pumps...
Usually they fail by leaking. So far as I know, overheating the system doesn't particularly make the pump fail any sooner. 240 water pumps have a small o-ring top gasket that mates to the head's underside; it likes to go bad and leak. The seal to cabin heater pipe at rear of water pump also can go bad but less often. Bearings will leak; the water comes out the rear of the pulley drive area - pulley assembly forms a shroud over the bearing area.
Lastly the pumps impeller blades can get corroded away to the point where they doesn't move much water. Or the coupling from pulley drive to impeller can go bad. You can test water flow by hooking up hoses and a water supply (barrel), if you want to take the time to do that. In my experience water pump replacement is a non-fun job so I'd be tempted to play with hoses instead - but some folks insist that water pump R+R is no hassle for them.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.
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