heat sensing transitor

im looking for a heat sensening transistor. can anyone recomend one and where i can find one. what i am doing is building a unit that will turn on my electric fan for my car at a temp that i want.

All transistors respond to temperature.

Their base-emitter voltage reduces by 2mV/degree C.

However, I think it more appropriate if you use a thermistor.

Those which are normally used in cars are immersed in the coolant and you should be able to get one from one of the accessory manufacturers.

i do work at one of the aftermarket places. the thing is, the old r&d guy dint leave the schematic for the controler. and he used a transitor for the thermister. but we have been haveing trouble with the unit lately. i have been trying to decipher the problem.

He could have possibly be using the base emitter junction as the thermister. The LM34 series temperature sensors are shaped like a TO92 case transistor.
The 1N914 diode has been used for a temperature sensor. When forward biased, the forward voltage varies with temperature. I don't think it is linear or has the range of the LM34 series.

well that is what it was a lm34. when i chiped all the epoxy away from the unit i just assumed it was a transitor. it had no markings on it. now all i have to do is draw up a simple on - off circuit.