Here's a dirty trick:
(not really recommended, for Testing and Educational Purposes only) heh
You can also install a switch under your dashboard wired to the Engine's Coolant Temp Sensor (located near the Thermostat), there are two wires, just cut one of those wires in the middle and attach your switch connections there. When you hit the switch the fan will start spinning and you'll notice the engine gaining a few rpms.
This can be considered cheating and it makes the car waste some extra fuel all the time the switch is thrown in, but in real life, it works, not the way it should but it does make your engine temp go low. God knows the implications and side effects of doing this, you're on your own under your own risk if you do it (I did it and 5k miles later my car seems happy tho, without any noticeable side effects so far) Not really recommended but if you're desperate this oughta do the trick till you install an aftermarket temp sensor or better.