Sounds like a bad fan clutch. Should have some resistance, especially if engine is overheated.

Even so, I'd clean the radiator fins with water from a garden hose first. That might improve the radiator's cooling performance enough to be OK again. Free up the radiator shroud for working room, and blast forward from rear side of radiator to blow out all the accumulated crud. Some folks might use compressed air but I'm not sure if it's a good idea. I'd let the engine cool off first too to avoid temperature shock.

Supposedly there's a "tropical" clutch out there but I don't know where.
But a new standard one should do the job if you need a fan clutch. I like fcpgroton.com for parts.

When removing fan/clutch assembly, you need a 10 mm. combination or open-end wrench due to the tight space. Crack nuts loose very s-l-o-w-l-y so you don't crack the stud loose instead. If nut remains stuck on stud and you start unthreading the stud, you'll be in for lots of fun with skinny needle-nose pliers + wrench getting things free due to the tight space in there. DAMHIK.

If you want you can put in an electric radiator fan instead.
I got mine from a dead 960; it's a strong 2-speed fan.
This would be a modification project; proceed at your own risk with the understanding that it might take many times longer than you estimate.
--
DAMHIK: Don't Ask Me How I Know - - - Sven: '89 245, IPD sways, electric rad. fan conversion, e-codes, 28+ mpg - auto tranny. 500 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).