Welcome- it's hard to tell if your fans are defective from the limited info you posted. The radiator fans turn on when a particular temp is reached. The easiest way to determine a problem is to pull codes from the BCM (body control module) section. Have you tried pulling any codes?
Also, depending on the last time you changed radiator fluid, you may have air trapped in the radiator that's causing overheating. Or your Z may have a defective radiator cap. How many miles are on your Z and when was the last time the fluid AND the radiator cap was changed?