Is there air in the cooling system? I had a situation where the radiator was leaking and even though I had filled both the radiator and the reservoir, the temperature sensor didn't give any readings when it should have. Probably an air bubble where the temperature sensor is. After I got the radiator fixed, a mechanic that I know gave me a tip on bleeding the system by leaving the radiator and reservoir caps open and letting the engine idle for ten minutes. The coolant poors out a bit but so does the air. After ten minutes let the engine cool down a bit before adding coolant to adjust the level. This worked fine for me.

The service manual says that you can test the temperature sensor by measuring the resistances in three different temperatures (each temperature giving different readings): 20, 80 and 110 degrees. From this I figured that 80 degrees must be when the fan should go on and 110 degrees when the engine overheating light turns on. I'm not sure of this though.

Have you tried letting the engine run on idle for 10-15 minutes? That should turn the fan on.

Jami