So I bought a 91 SE 5spd about 2 months ago with 138k on it. When I drive, the temp guage goes to the normal setting, but off and on, it will stay at 1/4 of the way up or even sit on the C mark. Is this a guage problem or sensor problem? Perhaps my thermostat needs replacing?

 

sounds like either a ground or the sensor gone bad.

 

You're in new jersy and it's december . . . it's really really cold outside right?

Odds are your car is being over-cooled. Mine does this and I live way down in memphis TN. Just put a piece of cardboard in front of the radiator until the temperature outside gets warmer. I keep one there during december and january most years.

 

Try tapping the dash area around the guage and see if the guage moves or not...mine did that once or twice but never did that again.

If thats ok than more than likely its the thermostat...

If u need a carboard then your thermostat is messed up...i drove through Minnesota last January through -35 winchill and temp of -11F in the night but the guage didnt even move from the center. that was after i had just replaced my faulty thermostat.