Have a 1997 Geo Prizm LSI (basically a Toyota Corolla) with the 1.8l engine. Recently the fan has started to stay on all the time. I can start the car cold in the morning and the fan automatically goes on and stays on, never shuts off. There are actually two fans but only one fan is going on and staying on. Other one only seems to kick on when engine is hot.
Any ideas on what would cause this and how to fix it?
If one fan only comes on when the engine tempo rises, the fan that's on all the time is probably the AC fan. It should come on when the AC is on, and is also controlled by a thermostat. Chances are, if it's on all the time, the thermostat is shorted out and causing the fan to come on. But, it should be energized only when the AC is on. Are you running the AC a lot?
Ok, same thing only different! The thermostat is probably stuck. Better stuck ON that stuck OFF!! I believe it is a sensor attatched to the side of the radiator. Follow the wiring from the fan, through the connector. One end will go to the voltage supply and the other goes throught the thermostat to ground.
With the engine cold, and the ignition in the on position (engine not running) check to see if you have 12 volts coming out of the sensor and going to the cooling fan. If so, then the sensor is bad. You should only have power going from the sensor to the cooling fan when the coolant is hot. By the way, make sure you stay clear of the fans when you're doing this!
Or, if you have an Ohm meter, remove the connector and measure across the terminals. There should be a high resistance (er, infinity...) Any less and the sensor is toast.
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