placing a resistor inline will delay or stop the fan from coming on at all. The fan switch itself is called a thermistor. The higher the temp the lower the resistence.
If you are not satisfied with "a" there are two options. Change the temp sending unit (gauge)or change the temp sending unit for the (pcm)
It is possible that one of these sensors is near the limit of acceptable range.

[This message has been edited by fuzzy (edited December 28, 2000).]