so ive got a 93 civic with a 99 engine, ive replaced the factory temperature sensor with an aftermarket one, ive noticed also that my radiator fan turns on after 40 miles per hour, and shuts off after you go below 35. it seems as it should just turn on when the car is at a set temperature so it gets up to ideal temperature to run more effectively

i guess my question is, is this right? or maybe i need to adjust or change something

 

The fan is activated by the temperature of the coolant leaving the radiator, not the temperature of the engine. After warm-up, engine temperature should stay constant through all driving conditions. The fan typically only needs to run when the car is not moving, so there is no airflow through the radiator. That causes the coolant to not lose heat as it flows through, thus the temperature in the lower hose increases. When it reaches about 160, the switch closes and the fan starts.

If it's having to run the fan on the highway, the radiator may not be working very well. Check if the fins on the outside have corroded and are falling off.