typ44TQ radiator fan question

[JordanVw@aol.com]

on my '86 5kTQ, the rad. fan does not come on, after the car is shut off, 
while hot.  for example, the rad. fan is running while the car is on, but 
when i shut the ignition off the fan doesnt even go to a lower speed like it 
should, and keep running, it just shuts off completely.   the only thing that 
continues to run is the injector blower fan that blows air up over the valve 
cover to the injectors.  any idea as to why the rad. fan doesnt cycle on and 
off after shutdown, but only runs while the ignition is on?

while the ignition is on, the fan works fine, and cycles on when needed.

TIA-
chris
'86 5kT, TQ