Nissan Repair: 99 Frontier temp gauge, radiator cap, fan clutch

Question
QUESTION: I have a '99 Frontier 4X4. When I am stopped or in slow traffic, the temp gauge goes up to the top. I think it would overheat if I didn't turn the heater on when it starts getting close to the top. Every year when the weather starts getting warmer, and I turn the heater indicator to cold(blue), this happens. I think maybe the fan in front of the radiator is not working, but I don't know how to test. I replaced thermostat, and it didn't change anything. Please help.

ANSWER: Cathy,

EIther the fan is not operating properly or the radiator is plugging up and needs to be cleaned or replaced.  Also, replace the radiator cap.  Without a pressurized system the engine will get hot, as you describe.  The cheap fix is to replace the cap first.  Second, check the fan, if electric, or if clutch type check for resistance, engine off, and hot.  The fan should be hard to spin.  If it freewheels, with little or no resistance, replace the fan clutch.  Remember that it is ten years old and the radiator could also be plugging up inside.

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QUESTION: I will replace the radiator cap as suggested, since it can't hurt anything. I checked the fan, and it spins pretty freely both directions. I think it is an electric fan. Do I replace the whole fan assemblly then, or what? Thanks so much for the help

Answer
Cathy,

If the fan is not connected to the engine by a shaft that means it is electric.  If it is electric you can check its operation by running the vehicle until it gets hot and see if the fan comes on.  Also, run the airconditioner and the computer should command the fan to come on.  If it comes on with the airconditioner and not all on its own, when the vehicle gets hot would mean the temperature sensor is defective for the computer to command operation or the relay that turns the fan on is defective.