Alfa Spiders & GTVs don't have radiators!
According to my Alfa Romeo Spider/GTV manual on CDROM, these models are unique because they have no radiator.
A search of the complete document for "radiator" or "coolant" reveals zero finds. The nearest I can find after an hour of browsing and searching is a page on the thermostat.
I've had a look inside the bonnet, and there is a large black thing at the front with rubber hoses going to it and lots of greenish fins disintegrating and falling off it, but it can't be a radiator as Alfa Romeo don't seem to fit them according to the manual.
I've been reading the threads in this forum all about short-lived Alfa radiators and their replacement, which is wonderful as without this forum we'd never have any information on them.
And I thought Haynes manuals were bad....