Dave- any chance you're radiator is gunked up or scaly inside?
I had a Quantum with that problem, drove me crazy.
She would overheat idling with the cooling fan blasting away.
I didn't have a spare Quantum rad and didn't feel like buying one for an
experiment, but I did have a rabbit unit laying around.
Hooked the rabbit rad up via long hoses outside the car to confirm the
problem.
I don't know if this is relevant to you're situation but hopefully it will
help.

(*snipped all to please the poor smucks who pay for data)