I just bought a '95 850 GLT wagon and the temp gauge has stopped working. I am wondering if I need a new sensor or thermostat or possibly both. All of the other dash gauges are working fine. When I start the car the temp gauge kicks up to the bottom line but never moves from that point. Very scary to not know what may be going on while I am driving the car. I searched through similar posts but none seem describe temp gauges that just do not show any temp at all. Any ideas? thanks!

Some of the laptop versions of OBD II scanners will give you temperature sensor readings. Mine does. (The very basic ones won't.) If the sensor works correctly, then you may have a bad ground on the guage.

While you are there, replace the thermostat, flush the system and replace the ECU sending unit and be done with it. Bottom of radiator on the drivers side should have a plug you can open to flush the system. Good luck.

I'm agree with Moregolf, I'd test the ECT sensor

Here's the specs:
Resistance @ Temperature
7300 ohms at 32 deg F
2800 ohms at 68 deg F
1200 ohms at 104 deg F
300 ohms at 176 deg F
150 ohms at 212 deg F
--
Ken

I would look at the sensor. I would guess the thermostat is not the issue.

To prove it:
Get a resistor about 300 ohms. (TV repair shop should have one for pennies)
Unplug the sensor (under the thermostat).
Connect the resistor in place of the sensor.
Switch on ignition.
The guage should read about mid scale.