I have to chirp in here about the suggestion one stick a towel or rubber hose in the fan while it is turning. I am a paramedic and attended to an incident a number of years ago where a mechanic was doing exactly that. I piece of the fan broke loose and struck him in the neck, taking out the carotid artery, internal and external jugulars. Needless to say, such an injury is not compatible with life. He bled out almost instantly.

The idea of heating the car up and shutting it down and testing if the fan has stiffened up seems way more sensible.

Play safe everyone