It's common for a clutch to not freewheel for a few seconds right after a cold start. The fluid settles while the clutch isn't spinning and takes a few moments to redistribute so the fan can freewheel. If it goes a couple of minutes without disengaging, look into it further. A feature of the clutch is that it disengages above 3000 rpm or so so the fan doesn't spin itself apart. Make sure you don't hear the clutch still engaged at higher rpms.

Sixto
87 300D