It's a NTC Negative Temperature Coefficient resistor. It does not produce voltage. As temperature goes up resistance goes down. It is the second resistor in a series circuit. The first resistor is mounted in the gauge and is fixed. As resistance in the temp sender changes with temperature the current in the circuit changes thus changing the magnetic field in the first resistor (gauge). The magnetic field acts on the metallic needle and moves the needle.

OK, technically it's a parallel circuit. The first branch is fixed and produces a fixed magnetic field that pulls the needle low (cold). The second branch has a fixed (apposing) resistor opposite the the first branch in the gauge and the the variable NTC down-circuit. As temperature rises, resistance lowers and current in the second branch goes up creating a stronger magnetic field and pulling the needle high (hot).