Temp. Sensor Operating Voltage., At what range does it operate?

[Damien95]

The temp. sensor that is fitted to the thermostat housing that sends the signal to the dash temp. gauge, at what voltage does it operate when cold and when hot?
Veichle is a 1995 Toyota Hilux Pick up. 2L-TE engine Auto. trans.
Thanks

[jaky cakes]

As far as I understand (which maybe wrong) the unit is basically a thermistor. A thermistor alters it's resistance (ohms) according to the temperature it is subjected to.
The voltage will always be the same (that of the vehicle 12 - 14v dc) but the resistance will alter. The dash gauge is basically a ohm meter displaying the resistance of the thermistor -calibrated to operating temperature extremes of the cooling system.
Is your gauge suspect or the sender unit?

[SoundsDigital]

Actually, I suspect the gauge is actually a voltmeter. However, the voltage at the thermistor will always be at the voltage of the battery if the wire is disconnected. The signal voltage is taken from between the thermistor and a fixed resistor. The fixed resistor has 12 volts supplied to the other side. As the resistance changes at the thermistor, the voltage drop across the thermistor and the fixed resistor is constant, but the potential difference at the sensor will change as the resistance of the thermistor changes.

[Damien95]

Actually, I suspect the gauge is actually a voltmeter. However, the voltage at the thermistor will always be at the voltage of the battery if the wire is disconnected. The signal voltage is taken from between the thermistor and a fixed resistor. The fixed resistor has 12 volts supplied to the other side. As the resistance changes at the thermistor, the voltage drop across the thermistor and the fixed resistor is constant, but the potential difference at the sensor will change as the resistance of the thermistor changes.

Yes that is how i believe it works.
My only problem is that i can't put a piece of wire in the clip that goes on the sensor so i can measure the voltage. It's made to measure.

[SoundsDigital]

Not sure how knowing the voltage is going to help you. If you short the wire to earth, it should send the gauge up to hot. If this is happening, then the sensor is most likely shot. If the gauge stays on cold with the wire earthed, then either the wiring is faulty or the gauge is gone. Hopefully this will help you. A thermistor is usually about 5 k at 25 degrees. This moves up or down when heat is applied or removed. The direction of travel depends on the type of thermistor. NTC or PTC. I would expect the one on an engine to be NTC and the resistance would reduce as the temperature increased. However, there are some surprises in the electrics on these vehicles.