I have a 1991 300zx non turbo and my fan will sometimes randomly go on and off. My fan just started working fine for about 4 days, it would blow more air as i accelerated( I did not do this for a before). For the 6 months a had the car the fan never function the way it did those 4 days. So now my car continues to overheat, and i think its because of the fan not functioning correctly. I changed the fan clutch twice and i dont think that may be the problem.

Hmm, does that year model have a secondary electric fan? I also wonder have you changed the thermostat? and is you car one that the cooling system has to have the air bleeded out if you cold fill? A bad thermostat that may not be opening all the way could cause your car to run war/hot as could a clogged radiator. the worst case would be if it ran hot enough you could have a leaking head gasket that will put "air" into you cooling system and cause the thermostat to not function properly....or if the cooling system is not bled then that would also cause an air pocket....sorry a few possible answers there....